Problem p03614 (C++)

Buggy submission (status: Time Limit Exceeded):
/*
 This code has been written by MinakoKojima, feel free to ask me question. Blog:
 http://www.shuizilong.com/house Template Date: 2015.10.12 Note: ...
 */

#pragma comment(linker, "/STACK:36777216")
// #pragma GCC optimize ("O2")
#define LOCAL
#include <algorithm>
#include <bitset>
#include <cassert>
#include <climits>
#include <cmath>
#include <complex>
#include <cstdio>
#include <cstring>
#include <ctime>
#include <fstream>
#include <functional>
#include <iomanip>
#include <iostream>
#include <list>
#include <map>
#include <numeric>
#include <queue>
#include <set>
#include <sstream>
#include <stack>
#include <string>
#include <vector>

// #include <tr1/unordered_set>
// #include <tr1/unordered_map>
// #include <array>

using namespace std;

#define REP(i, n) for (int i = 0; i < n; ++i)
#define FOR(i, a, b) for (int i = a; i < b; ++i)
#define DWN(i, b, a) for (int i = b - 1; i >= a; --i)
#define REP_1(i, n) for (int i = 1; i <= n; ++i)
#define FOR_1(i, a, b) for (int i = a; i <= b; ++i)
#define DWN_1(i, b, a) for (int i = b; i >= a; --i)
#define REP_C(i, n) for (int n____ = n, i = 0; i < n____; ++i)
#define FOR_C(i, a, b) for (int b____ = b, i = a; i < b____; ++i)
#define DWN_C(i, b, a) for (int a____ = a, i = b - 1; i >= a____; --i)
#define REP_N(i, n) for (i = 0; i < n; ++i)
#define FOR_N(i, a, b) for (i = a; i < b; ++i)
#define DWN_N(i, b, a) for (i = b - 1; i >= a; --i)
#define REP_1_C(i, n) for (int n____ = n, i = 1; i <= n____; ++i)
#define FOR_1_C(i, a, b) for (int b____ = b, i = a; i <= b____; ++i)
#define DWN_1_C(i, b, a) for (int a____ = a, i = b; i >= a____; --i)
#define REP_1_N(i, n) for (i = 1; i <= n; ++i)
#define FOR_1_N(i, a, b) for (i = a; i <= b; ++i)
#define DWN_1_N(i, b, a) for (i = b; i >= a; --i)
#define REP_C_N(i, n) for (int n____ = (i = 0, n); i < n____; ++i)
#define FOR_C_N(i, a, b) for (int b____ = (i = 0, b); i < b____; ++i)
#define DWN_C_N(i, b, a) for (int a____ = (i = b - 1, a); i >= a____; --i)
#define REP_1_C_N(i, n) for (int n____ = (i = 1, n); i <= n____; ++i)
#define FOR_1_C_N(i, a, b) for (int b____ = (i = a, b); i <= b____; ++i)
#define DWN_1_C_N(i, b, a) for (int a____ = (i = b, a); i >= a____; --i)

#define ECH(it, A)                                                             \
  for (__typeof((A).begin()) it = (A).begin(); it != (A).end(); ++it)
#define rECH(it, A)                                                            \
  for (__typeof((A).rbegin()) it = (A).rbegin(); it != (A).rend(); ++it)
#define REP_S(i, str) for (char *i = str; *i; ++i)
#define REP_L(i, hd, suc) for (int i = hd; i; i = suc[i])
#define REP_G(i, u) REP_L(i, hd[u], suc)
#define REP_SS(x, s) for (int x = s; x; x = (x - 1) & s)
#define DO(n) for (int ____n = n; ____n-- > 0;)
#define REP_2(i, j, n, m) REP(i, n) REP(j, m)
#define REP_2_1(i, j, n, m) REP_1(i, n) REP_1(j, m)
#define REP_3(i, j, k, n, m, l) REP(i, n) REP(j, m) REP(k, l)
#define REP_3_1(i, j, k, n, m, l) REP_1(i, n) REP_1(j, m) REP_1(k, l)
#define REP_4(i, j, k, ii, n, m, l, nn)                                        \
  REP(i, n) REP(j, m) REP(k, l) REP(ii, nn)
#define REP_4_1(i, j, k, ii, n, m, l, nn)                                      \
  REP_1(i, n) REP_1(j, m) REP_1(k, l) REP_1(ii, nn)

#define ALL(A) A.begin(), A.end()
#define LLA(A) A.rbegin(), A.rend()
#define CPY(A, B) memcpy(A, B, sizeof(A))
#define INS(A, P, B) A.insert(A.begin() + P, B)
#define ERS(A, P) A.erase(A.begin() + P)
#define LBD(A, x) (lower_bound(ALL(A), x) - A.begin())
#define UBD(A, x) (upper_bound(ALL(A), x) - A.begin())
#define CTN(T, x) (T.find(x) != T.end())
#define SZ(A) int((A).size())
#define PB push_back
#define MP(A, B) make_pair(A, B)
#define PTT pair<T, T>
#define Ts *this
#define rTs return Ts
#define fi first
#define se second
#define re real()
#define im imag()

#define Rush for (int ____T = RD(); ____T--;)
#define Display(A, n, m)                                                       \
  {                                                                            \
    REP(i, n) {                                                                \
      REP(j, m - 1) cout << A[i][j] << " ";                                    \
      cout << A[i][m - 1] << endl;                                             \
    }                                                                          \
  }
#define Display_1(A, n, m)                                                     \
  {                                                                            \
    REP_1(i, n) {                                                              \
      REP_1(j, m - 1) cout << A[i][j] << " ";                                  \
      cout << A[i][m] << endl;                                                 \
    }                                                                          \
  }

typedef long long LL;
// typedef long double DB;
typedef double DB;
typedef unsigned uint;
typedef unsigned long long uLL;

typedef vector<int> VI;
typedef vector<char> VC;
typedef vector<string> VS;
typedef vector<LL> VL;
typedef vector<DB> VF;
typedef set<int> SI;
typedef set<string> SS;
typedef map<int, int> MII;
typedef map<string, int> MSI;
typedef pair<int, int> PII;
typedef pair<LL, LL> PLL;
typedef vector<PII> VII;
typedef vector<VI> VVI;
typedef vector<VII> VVII;

template <class T> inline T &RD(T &);
template <class T> inline void OT(const T &);
// inline int RD(){int x; return RD(x);}
inline LL RD() {
  LL x;
  return RD(x);
}
inline DB &RF(DB &);
inline DB RF() {
  DB x;
  return RF(x);
}
inline char *RS(char *s);
inline char &RC(char &c);
inline char RC();
inline char &RC(char &c) {
  scanf(" %c", &c);
  return c;
}
inline char RC() {
  char c;
  return RC(c);
}
// inline char& RC(char &c){c = getchar(); return c;}
// inline char RC(){return getchar();}

template <class T> inline T &RDD(T &);
inline LL RDD() {
  LL x;
  return RDD(x);
}

template <class T0, class T1> inline T0 &RD(T0 &x0, T1 &x1) {
  RD(x0), RD(x1);
  return x0;
}
template <class T0, class T1, class T2> inline T0 &RD(T0 &x0, T1 &x1, T2 &x2) {
  RD(x0), RD(x1), RD(x2);
  return x0;
}
template <class T0, class T1, class T2, class T3>
inline T0 &RD(T0 &x0, T1 &x1, T2 &x2, T3 &x3) {
  RD(x0), RD(x1), RD(x2), RD(x3);
  return x0;
}
template <class T0, class T1, class T2, class T3, class T4>
inline T0 &RD(T0 &x0, T1 &x1, T2 &x2, T3 &x3, T4 &x4) {
  RD(x0), RD(x1), RD(x2), RD(x3), RD(x4);
  return x0;
}
template <class T0, class T1, class T2, class T3, class T4, class T5>
inline T0 &RD(T0 &x0, T1 &x1, T2 &x2, T3 &x3, T4 &x4, T5 &x5) {
  RD(x0), RD(x1), RD(x2), RD(x3), RD(x4), RD(x5);
  return x0;
}
template <class T0, class T1, class T2, class T3, class T4, class T5, class T6>
inline T0 &RD(T0 &x0, T1 &x1, T2 &x2, T3 &x3, T4 &x4, T5 &x5, T6 &x6) {
  RD(x0), RD(x1), RD(x2), RD(x3), RD(x4), RD(x5), RD(x6);
  return x0;
}
template <class T0, class T1> inline void OT(const T0 &x0, const T1 &x1) {
  OT(x0), OT(x1);
}
template <class T0, class T1, class T2>
inline void OT(const T0 &x0, const T1 &x1, const T2 &x2) {
  OT(x0), OT(x1), OT(x2);
}
template <class T0, class T1, class T2, class T3>
inline void OT(const T0 &x0, const T1 &x1, const T2 &x2, const T3 &x3) {
  OT(x0), OT(x1), OT(x2), OT(x3);
}
template <class T0, class T1, class T2, class T3, class T4>
inline void OT(const T0 &x0, const T1 &x1, const T2 &x2, const T3 &x3,
               const T4 &x4) {
  OT(x0), OT(x1), OT(x2), OT(x3), OT(x4);
}
template <class T0, class T1, class T2, class T3, class T4, class T5>
inline void OT(const T0 &x0, const T1 &x1, const T2 &x2, const T3 &x3,
               const T4 &x4, const T5 &x5) {
  OT(x0), OT(x1), OT(x2), OT(x3), OT(x4), OT(x5);
}
template <class T0, class T1, class T2, class T3, class T4, class T5, class T6>
inline void OT(const T0 &x0, const T1 &x1, const T2 &x2, const T3 &x3,
               const T4 &x4, const T5 &x5, const T6 &x6) {
  OT(x0), OT(x1), OT(x2), OT(x3), OT(x4), OT(x5), OT(x6);
}
inline char &RC(char &a, char &b) {
  RC(a), RC(b);
  return a;
}
inline char &RC(char &a, char &b, char &c) {
  RC(a), RC(b), RC(c);
  return a;
}
inline char &RC(char &a, char &b, char &c, char &d) {
  RC(a), RC(b), RC(c), RC(d);
  return a;
}
inline char &RC(char &a, char &b, char &c, char &d, char &e) {
  RC(a), RC(b), RC(c), RC(d), RC(e);
  return a;
}
inline char &RC(char &a, char &b, char &c, char &d, char &e, char &f) {
  RC(a), RC(b), RC(c), RC(d), RC(e), RC(f);
  return a;
}
inline char &RC(char &a, char &b, char &c, char &d, char &e, char &f, char &g) {
  RC(a), RC(b), RC(c), RC(d), RC(e), RC(f), RC(g);
  return a;
}
inline DB &RF(DB &a, DB &b) {
  RF(a), RF(b);
  return a;
}
inline DB &RF(DB &a, DB &b, DB &c) {
  RF(a), RF(b), RF(c);
  return a;
}
inline DB &RF(DB &a, DB &b, DB &c, DB &d) {
  RF(a), RF(b), RF(c), RF(d);
  return a;
}
inline DB &RF(DB &a, DB &b, DB &c, DB &d, DB &e) {
  RF(a), RF(b), RF(c), RF(d), RF(e);
  return a;
}
inline DB &RF(DB &a, DB &b, DB &c, DB &d, DB &e, DB &f) {
  RF(a), RF(b), RF(c), RF(d), RF(e), RF(f);
  return a;
}
inline DB &RF(DB &a, DB &b, DB &c, DB &d, DB &e, DB &f, DB &g) {
  RF(a), RF(b), RF(c), RF(d), RF(e), RF(f), RF(g);
  return a;
}
inline void RS(char *s1, char *s2) { RS(s1), RS(s2); }
inline void RS(char *s1, char *s2, char *s3) { RS(s1), RS(s2), RS(s3); }
template <class T0, class T1> inline T0 &RDD(T0 &a, T1 &b) {
  RDD(a), RDD(b);
  return a;
}
template <class T0, class T1, class T2> inline T1 &RDD(T0 &a, T1 &b, T2 &c) {
  RDD(a), RDD(b), RDD(c);
  return a;
}

template <class T> inline void RST(T &A) { memset(A, 0, sizeof(A)); }
template <class T> inline void FLC(T &A, int x) { memset(A, x, sizeof(A)); }
template <class T> inline void CLR(T &A) { A.clear(); }

template <class T0, class T1> inline void RST(T0 &A0, T1 &A1) {
  RST(A0), RST(A1);
}
template <class T0, class T1, class T2>
inline void RST(T0 &A0, T1 &A1, T2 &A2) {
  RST(A0), RST(A1), RST(A2);
}
template <class T0, class T1, class T2, class T3>
inline void RST(T0 &A0, T1 &A1, T2 &A2, T3 &A3) {
  RST(A0), RST(A1), RST(A2), RST(A3);
}
template <class T0, class T1, class T2, class T3, class T4>
inline void RST(T0 &A0, T1 &A1, T2 &A2, T3 &A3, T4 &A4) {
  RST(A0), RST(A1), RST(A2), RST(A3), RST(A4);
}
template <class T0, class T1, class T2, class T3, class T4, class T5>
inline void RST(T0 &A0, T1 &A1, T2 &A2, T3 &A3, T4 &A4, T5 &A5) {
  RST(A0), RST(A1), RST(A2), RST(A3), RST(A4), RST(A5);
}
template <class T0, class T1, class T2, class T3, class T4, class T5, class T6>
inline void RST(T0 &A0, T1 &A1, T2 &A2, T3 &A3, T4 &A4, T5 &A5, T6 &A6) {
  RST(A0), RST(A1), RST(A2), RST(A3), RST(A4), RST(A5), RST(A6);
}
template <class T0, class T1> inline void FLC(T0 &A0, T1 &A1, int x) {
  FLC(A0, x), FLC(A1, x);
}
template <class T0, class T1, class T2>
inline void FLC(T0 &A0, T1 &A1, T2 &A2, int x) {
  FLC(A0, x), FLC(A1, x), FLC(A2, x);
}
template <class T0, class T1, class T2, class T3>
inline void FLC(T0 &A0, T1 &A1, T2 &A2, T3 &A3, int x) {
  FLC(A0, x), FLC(A1, x), FLC(A2, x), FLC(A3, x);
}
template <class T0, class T1, class T2, class T3, class T4>
inline void FLC(T0 &A0, T1 &A1, T2 &A2, T3 &A3, T4 &A4, int x) {
  FLC(A0, x), FLC(A1, x), FLC(A2, x), FLC(A3, x), FLC(A4, x);
}
template <class T0, class T1, class T2, class T3, class T4, class T5>
inline void FLC(T0 &A0, T1 &A1, T2 &A2, T3 &A3, T4 &A4, T5 &A5, int x) {
  FLC(A0, x), FLC(A1, x), FLC(A2, x), FLC(A3, x), FLC(A4, x), FLC(A5, x);
}
template <class T0, class T1, class T2, class T3, class T4, class T5, class T6>
inline void FLC(T0 &A0, T1 &A1, T2 &A2, T3 &A3, T4 &A4, T5 &A5, T6 &A6, int x) {
  FLC(A0, x), FLC(A1, x), FLC(A2, x), FLC(A3, x), FLC(A4, x), FLC(A5, x),
      FLC(A6, x);
}
template <class T> inline void CLR(priority_queue<T, vector<T>, less<T>> &Q) {
  while (!Q.empty())
    Q.pop();
}
template <class T>
inline void CLR(priority_queue<T, vector<T>, greater<T>> &Q) {
  while (!Q.empty())
    Q.pop();
}
template <class T> inline void CLR(stack<T> &S) {
  while (!S.empty())
    S.pop();
}
template <class T> inline void CLR(queue<T> &Q) {
  while (!Q.empty())
    Q.pop();
}

template <class T0, class T1> inline void CLR(T0 &A0, T1 &A1) {
  CLR(A0), CLR(A1);
}
template <class T0, class T1, class T2>
inline void CLR(T0 &A0, T1 &A1, T2 &A2) {
  CLR(A0), CLR(A1), CLR(A2);
}
template <class T0, class T1, class T2, class T3>
inline void CLR(T0 &A0, T1 &A1, T2 &A2, T3 &A3) {
  CLR(A0), CLR(A1), CLR(A2), CLR(A3);
}
template <class T0, class T1, class T2, class T3, class T4>
inline void CLR(T0 &A0, T1 &A1, T2 &A2, T3 &A3, T4 &A4) {
  CLR(A0), CLR(A1), CLR(A2), CLR(A3), CLR(A4);
}
template <class T0, class T1, class T2, class T3, class T4, class T5>
inline void CLR(T0 &A0, T1 &A1, T2 &A2, T3 &A3, T4 &A4, T5 &A5) {
  CLR(A0), CLR(A1), CLR(A2), CLR(A3), CLR(A4), CLR(A5);
}
template <class T0, class T1, class T2, class T3, class T4, class T5, class T6>
inline void CLR(T0 &A0, T1 &A1, T2 &A2, T3 &A3, T4 &A4, T5 &A5, T6 &A6) {
  CLR(A0), CLR(A1), CLR(A2), CLR(A3), CLR(A4), CLR(A5), CLR(A6);
}
template <class T> inline void CLR(T &A, int n) { REP(i, n) CLR(A[i]); }

template <class T> inline bool EPT(T &a) { return a.empty(); }
template <class T> inline T &SRT(T &A) {
  sort(ALL(A));
  return A;
}
template <class T, class C> inline T &SRT(T &A, C cmp) {
  sort(ALL(A), cmp);
  return A;
}
template <class T> inline T &RVS(T &A) {
  reverse(ALL(A));
  return A;
}
template <class T> inline T &UNQQ(T &A) {
  A.resize(unique(ALL(A)) - A.begin());
  return A;
}
template <class T> inline T &UNQ(T &A) {
  SRT(A);
  return UNQQ(A);
}
template <class T, class C> inline T &UNQ(T &A, C cmp) {
  SRT(A, cmp);
  return UNQQ(A);
}

//}

/** Constant List .. **/ //{

const int MOD = int(1e9) + 7;
const int INF = 0x3f3f3f3f;
const LL INFF = 0x3f3f3f3f3f3f3f3fLL;
const DB EPS = 1e-9;
const DB OO = 1e20;
const DB PI = acos(-1.0); // M_PI;

const int dx[] = {-1, 0, 1, 0};
const int dy[] = {0, 1, 0, -1};

//}

/** Add On .. **/ //{
// <<= '0. Nichi Joo ., //{

template <class T> inline bool checkMin(T &a, const T b) {
  return b < a ? a = b, 1 : 0;
}
template <class T> inline bool checkMax(T &a, const T b) {
  return a < b ? a = b, 1 : 0;
}
template <class T, class C> inline bool checkUpd(T &a, const T b, C c) {
  return c(b, a) ? a = b, 1 : 0;
}
template <class T> inline T min(T a, T b, T c) { return min(min(a, b), c); }
template <class T> inline T max(T a, T b, T c) { return max(max(a, b), c); }
template <class T> inline T min(T a, T b, T c, T d) {
  return min(min(a, b), min(c, d));
}
template <class T> inline T max(T a, T b, T c, T d) {
  return max(max(a, b), max(c, d));
}
template <class T> inline T min(T a, T b, T c, T d, T e) {
  return min(min(min(a, b), min(c, d)), e);
}
template <class T> inline T max(T a, T b, T c, T d, T e) {
  return max(max(max(a, b), max(c, d)), e);
}
template <class T> inline T sqr(T a) { return a * a; }
template <class T> inline T cub(T a) { return a * a * a; }
template <class T> inline T ceil(T x, T y) { return (x - 1) / y + 1; }
template <class T> T abs(T x) { return x > 0 ? x : -x; }
inline int sgn(DB x) { return x < -EPS ? -1 : x > EPS; }
inline int sgn(DB x, DB y) { return sgn(x - y); }

inline DB cos(DB a, DB b, DB c) {
  return (sqr(a) + sqr(b) - sqr(c)) / (2 * a * b);
}
inline DB cot(DB x) { return 1. / tan(x); };
inline DB sec(DB x) { return 1. / cos(x); };
inline DB csc(DB x) { return 1. / sin(x); };

//}
// <<= '1. Bitwise Operation ., //{
namespace BO {

inline bool _1(int x, int i) { return bool(x & 1 << i); }
inline bool _1(LL x, int i) { return bool(x & 1LL << i); }
inline LL _1(int i) { return 1LL << i; }
inline LL _U(int i) { return _1(i) - 1; };

inline int reverse_bits(int x) {
  x = ((x >> 1) & 0x55555555) | ((x << 1) & 0xaaaaaaaa);
  x = ((x >> 2) & 0x33333333) | ((x << 2) & 0xcccccccc);
  x = ((x >> 4) & 0x0f0f0f0f) | ((x << 4) & 0xf0f0f0f0);
  x = ((x >> 8) & 0x00ff00ff) | ((x << 8) & 0xff00ff00);
  x = ((x >> 16) & 0x0000ffff) | ((x << 16) & 0xffff0000);
  return x;
}

inline LL reverse_bits(LL x) {
  x = ((x >> 1) & 0x5555555555555555LL) | ((x << 1) & 0xaaaaaaaaaaaaaaaaLL);
  x = ((x >> 2) & 0x3333333333333333LL) | ((x << 2) & 0xccccccccccccccccLL);
  x = ((x >> 4) & 0x0f0f0f0f0f0f0f0fLL) | ((x << 4) & 0xf0f0f0f0f0f0f0f0LL);
  x = ((x >> 8) & 0x00ff00ff00ff00ffLL) | ((x << 8) & 0xff00ff00ff00ff00LL);
  x = ((x >> 16) & 0x0000ffff0000ffffLL) | ((x << 16) & 0xffff0000ffff0000LL);
  x = ((x >> 32) & 0x00000000ffffffffLL) | ((x << 32) & 0xffffffff00000000LL);
  return x;
}

template <class T> inline bool odd(T x) { return x & 1; }
template <class T> inline bool even(T x) { return !odd(x); }
template <class T> inline T low_bit(T x) { return x & -x; }
template <class T> inline T high_bit(T x) {
  T p = low_bit(x);
  while (p != x)
    x -= p, p = low_bit(x);
  return p;
}
template <class T> inline T cover_bit(T x) {
  T p = 1;
  while (p < x)
    p <<= 1;
  return p;
}
template <class T> inline int cover_idx(T x) {
  int p = 0;
  while (_1(p) < x)
    ++p;
  return p;
}

inline int clz(int x) { return __builtin_clz(x); }
inline int clz(LL x) { return __builtin_clzll(x); }
inline int ctz(int x) { return __builtin_ctz(x); }
inline int ctz(LL x) { return __builtin_ctzll(x); }
inline int lg2(int x) { return !x ? -1 : 31 - clz(x); }
inline int lg2(LL x) { return !x ? -1 : 63 - clz(x); }
inline int low_idx(int x) { return !x ? -1 : ctz(x); }
inline int low_idx(LL x) { return !x ? -1 : ctz(x); }
inline int high_idx(int x) { return lg2(x); }
inline int high_idx(LL x) { return lg2(x); }
inline int parity(int x) { return __builtin_parity(x); }
inline int parity(LL x) { return __builtin_parityll(x); }
inline int count_bits(int x) { return __builtin_popcount(x); }
inline int count_bits(LL x) { return __builtin_popcountll(x); }

} // namespace BO
using namespace BO; //}

// <<= '2. Number Theory .,//{
namespace NT {
#define gcd __gcd
inline LL lcm(LL a, LL b) { return a * b / gcd(a, b); }

inline void INC(int &a, int b) {
  a += b;
  if (a >= MOD)
    a -= MOD;
}
inline int sum(int a, int b) {
  a += b;
  if (a >= MOD)
    a -= MOD;
  return a;
}

/* 模数两倍刚好超 int 时。
 inline int sum(uint a, int b){a += b; a %= MOD;if (a < 0) a += MOD; return a;}
 inline void INC(int &a, int b){a = sum(a, b);}
 */

inline void DEC(int &a, int b) {
  a -= b;
  if (a < 0)
    a += MOD;
}
inline int dff(int a, int b) {
  a -= b;
  if (a < 0)
    a += MOD;
  return a;
}
inline void MUL(int &a, int b) { a = (LL)a * b % MOD; }
// inline int pdt(int a, int b){return (LL)a * b % MOD;}
inline int pdt(int x, int y) {
  int ret;
  __asm__ __volatile__("\tmull %%ebx\n\tdivl %%ecx\n"
                       : "=d"(ret)
                       : "a"(x), "b"(y), "c"(MOD));
  return ret;
}

inline int gcd(int m, int n, int &x, int &y) {

  x = 1, y = 0;
  int xx = 0, yy = 1, q;

  while (1) {
    q = m / n, m %= n;
    if (!m) {
      x = xx, y = yy;
      return n;
    }
    DEC(x, pdt(q, xx)), DEC(y, pdt(q, yy));
    q = n / m, n %= m;
    if (!n)
      return m;
    DEC(xx, pdt(q, x)), DEC(yy, pdt(q, y));
  }
}

inline int sum(int a, int b, int c) { return sum(a, sum(b, c)); }
inline int sum(int a, int b, int c, int d) { return sum(sum(a, b), sum(c, d)); }
inline int pdt(int a, int b, int c) { return pdt(a, pdt(b, c)); }
inline int pdt(int a, int b, int c, int d) { return pdt(pdt(a, b), pdt(c, d)); }

inline int pow(int a, LL b) {
  int c(1);
  while (b) {
    if (b & 1)
      MUL(c, a);
    MUL(a, a), b >>= 1;
  }
  return c;
}

template <class T> inline T pow(T a, LL b) {
  T c(1);
  while (b) {
    if (b & 1)
      c *= a;
    a *= a, b >>= 1;
  }
  return c;
}

template <class T> inline T pow(T a, int b) { return pow(a, (LL)b); }

inline int _I(int b) {
  int a = MOD, x1 = 0, x2 = 1, q;
  while (1) {
    q = a / b, a %= b;
    if (!a)
      return x2;
    DEC(x1, pdt(q, x2));

    q = b / a, b %= a;
    if (!b)
      return x1;
    DEC(x2, pdt(q, x1));
  }
}

inline void DIV(int &a, int b) { MUL(a, _I(b)); }
inline int qtt(int a, int b) { return pdt(a, _I(b)); }

struct Int {
  int val;

  operator int() const { return val; }

  Int(int _val = 0) : val(_val) {
    val %= MOD;
    if (val < 0)
      val += MOD;
  }
  Int(LL _val) : val(_val) {
    _val %= MOD;
    if (_val < 0)
      _val += MOD;
    val = _val;
  }

  Int &operator+=(const int &rhs) {
    INC(val, rhs);
    rTs;
  }
  Int operator+(const int &rhs) const { return sum(val, rhs); }
  Int &operator-=(const int &rhs) {
    DEC(val, rhs);
    rTs;
  }
  Int operator-(const int &rhs) const { return dff(val, rhs); }
  Int &operator*=(const int &rhs) {
    MUL(val, rhs);
    rTs;
  }
  Int operator*(const int &rhs) const { return pdt(val, rhs); }
  Int &operator/=(const int &rhs) {
    DIV(val, rhs);
    rTs;
  }
  Int operator/(const int &rhs) const { return qtt(val, rhs); }
  Int operator-() const { return MOD - *this; }
};

} // namespace NT
using namespace NT; //}

//}

/** I/O Accelerator Interface .. **/ //{
#define g (c = getchar())
#define d isdigit(g)
#define p x = x * 10 + c - '0'
#define n x = x * 10 + '0' - c
#define pp l /= 10, p
#define nn l /= 10, n
template <class T> inline T &RD(T &x) {
  char c;
  while (!d)
    ;
  x = c - '0';
  while (d)
    p;
  return x;
}
template <class T> inline T &RDD(T &x) {
  char c;
  while (g, c != '-' && !isdigit(c))
    ;
  if (c == '-') {
    x = '0' - g;
    while (d)
      n;
  } else {
    x = c - '0';
    while (d)
      p;
  }
  return x;
}
inline DB &RF(DB &x) {
  // scanf("%lf", &x);
  char c;
  while (g, c != '-' && c != '.' && !isdigit(c))
    ;
  if (c == '-')
    if (g == '.') {
      x = 0;
      DB l = 1;
      while (d)
        nn;
      x *= l;
    } else {
      x = '0' - c;
      while (d)
        n;
      if (c == '.') {
        DB l = 1;
        while (d)
          nn;
        x *= l;
      }
    }
  else if (c == '.') {
    x = 0;
    DB l = 1;
    while (d)
      pp;
    x *= l;
  } else {
    x = c - '0';
    while (d)
      p;
    if (c == '.') {
      DB l = 1;
      while (d)
        pp;
      x *= l;
    }
  }
  return x;
}
#undef nn
#undef pp
#undef n
#undef p
#undef d
#undef g
inline char *RS(char *s) {
  // gets(s);
  scanf("%s", s);
  return s;
}

LL last_ans;
int Case;
template <class T> inline void OT(const T &x) {
  // printf("Case #%d: ", ++Case);
  // printf("%lld\n", x);
  // printf("%I64d\n", x);
  // printf("%.9f\n", x);
  // printf("%d\n", x);
  cout << x << endl;
  // last_ans = x;
}

//}/*
//..................................................................................................................................
//*/

const int N = int(1e5) + 9;
int P[N], n;

int main() {

#ifndef ONLINE_JUDGE
  freopen("/users/minakokojima/ACM-Training/Workspace/in.txt", "r", stdin);
  // freopen("/users/minakokojima/ACM-Training/Workspace/out.txt", "w", stdout);
#endif

  RD(n);
  REP_1(i, n) RD(P[i]);
  int z = 0;
  REP_1(i, n) if (P[i] == i) {
    ++z;
    if (i != n)
      swap(P[i], P[i + 1]);
    else
      swap(P[i], P[i - 1]);
  }
  cout << z << endl;
}


Fixed submission:
/*
 This code has been written by MinakoKojima, feel free to ask me question. Blog:
 http://www.shuizilong.com/house Template Date: 2015.10.12 Note: ...
 */

#pragma comment(linker, "/STACK:36777216")
// #pragma GCC optimize ("O2")
#define LOCAL
#include <algorithm>
#include <bitset>
#include <cassert>
#include <climits>
#include <cmath>
#include <complex>
#include <cstdio>
#include <cstring>
#include <ctime>
#include <fstream>
#include <functional>
#include <iomanip>
#include <iostream>
#include <list>
#include <map>
#include <numeric>
#include <queue>
#include <set>
#include <sstream>
#include <stack>
#include <string>
#include <vector>

// #include <tr1/unordered_set>
// #include <tr1/unordered_map>
// #include <array>

using namespace std;

#define REP(i, n) for (int i = 0; i < n; ++i)
#define FOR(i, a, b) for (int i = a; i < b; ++i)
#define DWN(i, b, a) for (int i = b - 1; i >= a; --i)
#define REP_1(i, n) for (int i = 1; i <= n; ++i)
#define FOR_1(i, a, b) for (int i = a; i <= b; ++i)
#define DWN_1(i, b, a) for (int i = b; i >= a; --i)
#define REP_C(i, n) for (int n____ = n, i = 0; i < n____; ++i)
#define FOR_C(i, a, b) for (int b____ = b, i = a; i < b____; ++i)
#define DWN_C(i, b, a) for (int a____ = a, i = b - 1; i >= a____; --i)
#define REP_N(i, n) for (i = 0; i < n; ++i)
#define FOR_N(i, a, b) for (i = a; i < b; ++i)
#define DWN_N(i, b, a) for (i = b - 1; i >= a; --i)
#define REP_1_C(i, n) for (int n____ = n, i = 1; i <= n____; ++i)
#define FOR_1_C(i, a, b) for (int b____ = b, i = a; i <= b____; ++i)
#define DWN_1_C(i, b, a) for (int a____ = a, i = b; i >= a____; --i)
#define REP_1_N(i, n) for (i = 1; i <= n; ++i)
#define FOR_1_N(i, a, b) for (i = a; i <= b; ++i)
#define DWN_1_N(i, b, a) for (i = b; i >= a; --i)
#define REP_C_N(i, n) for (int n____ = (i = 0, n); i < n____; ++i)
#define FOR_C_N(i, a, b) for (int b____ = (i = 0, b); i < b____; ++i)
#define DWN_C_N(i, b, a) for (int a____ = (i = b - 1, a); i >= a____; --i)
#define REP_1_C_N(i, n) for (int n____ = (i = 1, n); i <= n____; ++i)
#define FOR_1_C_N(i, a, b) for (int b____ = (i = a, b); i <= b____; ++i)
#define DWN_1_C_N(i, b, a) for (int a____ = (i = b, a); i >= a____; --i)

#define ECH(it, A)                                                             \
  for (__typeof((A).begin()) it = (A).begin(); it != (A).end(); ++it)
#define rECH(it, A)                                                            \
  for (__typeof((A).rbegin()) it = (A).rbegin(); it != (A).rend(); ++it)
#define REP_S(i, str) for (char *i = str; *i; ++i)
#define REP_L(i, hd, suc) for (int i = hd; i; i = suc[i])
#define REP_G(i, u) REP_L(i, hd[u], suc)
#define REP_SS(x, s) for (int x = s; x; x = (x - 1) & s)
#define DO(n) for (int ____n = n; ____n-- > 0;)
#define REP_2(i, j, n, m) REP(i, n) REP(j, m)
#define REP_2_1(i, j, n, m) REP_1(i, n) REP_1(j, m)
#define REP_3(i, j, k, n, m, l) REP(i, n) REP(j, m) REP(k, l)
#define REP_3_1(i, j, k, n, m, l) REP_1(i, n) REP_1(j, m) REP_1(k, l)
#define REP_4(i, j, k, ii, n, m, l, nn)                                        \
  REP(i, n) REP(j, m) REP(k, l) REP(ii, nn)
#define REP_4_1(i, j, k, ii, n, m, l, nn)                                      \
  REP_1(i, n) REP_1(j, m) REP_1(k, l) REP_1(ii, nn)

#define ALL(A) A.begin(), A.end()
#define LLA(A) A.rbegin(), A.rend()
#define CPY(A, B) memcpy(A, B, sizeof(A))
#define INS(A, P, B) A.insert(A.begin() + P, B)
#define ERS(A, P) A.erase(A.begin() + P)
#define LBD(A, x) (lower_bound(ALL(A), x) - A.begin())
#define UBD(A, x) (upper_bound(ALL(A), x) - A.begin())
#define CTN(T, x) (T.find(x) != T.end())
#define SZ(A) int((A).size())
#define PB push_back
#define MP(A, B) make_pair(A, B)
#define PTT pair<T, T>
#define Ts *this
#define rTs return Ts
#define fi first
#define se second
#define re real()
#define im imag()

#define Rush for (int ____T = RD(); ____T--;)
#define Display(A, n, m)                                                       \
  {                                                                            \
    REP(i, n) {                                                                \
      REP(j, m - 1) cout << A[i][j] << " ";                                    \
      cout << A[i][m - 1] << endl;                                             \
    }                                                                          \
  }
#define Display_1(A, n, m)                                                     \
  {                                                                            \
    REP_1(i, n) {                                                              \
      REP_1(j, m - 1) cout << A[i][j] << " ";                                  \
      cout << A[i][m] << endl;                                                 \
    }                                                                          \
  }

typedef long long LL;
// typedef long double DB;
typedef double DB;
typedef unsigned uint;
typedef unsigned long long uLL;

typedef vector<int> VI;
typedef vector<char> VC;
typedef vector<string> VS;
typedef vector<LL> VL;
typedef vector<DB> VF;
typedef set<int> SI;
typedef set<string> SS;
typedef map<int, int> MII;
typedef map<string, int> MSI;
typedef pair<int, int> PII;
typedef pair<LL, LL> PLL;
typedef vector<PII> VII;
typedef vector<VI> VVI;
typedef vector<VII> VVII;

template <class T> inline T &RD(T &);
template <class T> inline void OT(const T &);
// inline int RD(){int x; return RD(x);}
inline LL RD() {
  LL x;
  return RD(x);
}
inline DB &RF(DB &);
inline DB RF() {
  DB x;
  return RF(x);
}
inline char *RS(char *s);
inline char &RC(char &c);
inline char RC();
inline char &RC(char &c) {
  scanf(" %c", &c);
  return c;
}
inline char RC() {
  char c;
  return RC(c);
}
// inline char& RC(char &c){c = getchar(); return c;}
// inline char RC(){return getchar();}

template <class T> inline T &RDD(T &);
inline LL RDD() {
  LL x;
  return RDD(x);
}

template <class T0, class T1> inline T0 &RD(T0 &x0, T1 &x1) {
  RD(x0), RD(x1);
  return x0;
}
template <class T0, class T1, class T2> inline T0 &RD(T0 &x0, T1 &x1, T2 &x2) {
  RD(x0), RD(x1), RD(x2);
  return x0;
}
template <class T0, class T1, class T2, class T3>
inline T0 &RD(T0 &x0, T1 &x1, T2 &x2, T3 &x3) {
  RD(x0), RD(x1), RD(x2), RD(x3);
  return x0;
}
template <class T0, class T1, class T2, class T3, class T4>
inline T0 &RD(T0 &x0, T1 &x1, T2 &x2, T3 &x3, T4 &x4) {
  RD(x0), RD(x1), RD(x2), RD(x3), RD(x4);
  return x0;
}
template <class T0, class T1, class T2, class T3, class T4, class T5>
inline T0 &RD(T0 &x0, T1 &x1, T2 &x2, T3 &x3, T4 &x4, T5 &x5) {
  RD(x0), RD(x1), RD(x2), RD(x3), RD(x4), RD(x5);
  return x0;
}
template <class T0, class T1, class T2, class T3, class T4, class T5, class T6>
inline T0 &RD(T0 &x0, T1 &x1, T2 &x2, T3 &x3, T4 &x4, T5 &x5, T6 &x6) {
  RD(x0), RD(x1), RD(x2), RD(x3), RD(x4), RD(x5), RD(x6);
  return x0;
}
template <class T0, class T1> inline void OT(const T0 &x0, const T1 &x1) {
  OT(x0), OT(x1);
}
template <class T0, class T1, class T2>
inline void OT(const T0 &x0, const T1 &x1, const T2 &x2) {
  OT(x0), OT(x1), OT(x2);
}
template <class T0, class T1, class T2, class T3>
inline void OT(const T0 &x0, const T1 &x1, const T2 &x2, const T3 &x3) {
  OT(x0), OT(x1), OT(x2), OT(x3);
}
template <class T0, class T1, class T2, class T3, class T4>
inline void OT(const T0 &x0, const T1 &x1, const T2 &x2, const T3 &x3,
               const T4 &x4) {
  OT(x0), OT(x1), OT(x2), OT(x3), OT(x4);
}
template <class T0, class T1, class T2, class T3, class T4, class T5>
inline void OT(const T0 &x0, const T1 &x1, const T2 &x2, const T3 &x3,
               const T4 &x4, const T5 &x5) {
  OT(x0), OT(x1), OT(x2), OT(x3), OT(x4), OT(x5);
}
template <class T0, class T1, class T2, class T3, class T4, class T5, class T6>
inline void OT(const T0 &x0, const T1 &x1, const T2 &x2, const T3 &x3,
               const T4 &x4, const T5 &x5, const T6 &x6) {
  OT(x0), OT(x1), OT(x2), OT(x3), OT(x4), OT(x5), OT(x6);
}
inline char &RC(char &a, char &b) {
  RC(a), RC(b);
  return a;
}
inline char &RC(char &a, char &b, char &c) {
  RC(a), RC(b), RC(c);
  return a;
}
inline char &RC(char &a, char &b, char &c, char &d) {
  RC(a), RC(b), RC(c), RC(d);
  return a;
}
inline char &RC(char &a, char &b, char &c, char &d, char &e) {
  RC(a), RC(b), RC(c), RC(d), RC(e);
  return a;
}
inline char &RC(char &a, char &b, char &c, char &d, char &e, char &f) {
  RC(a), RC(b), RC(c), RC(d), RC(e), RC(f);
  return a;
}
inline char &RC(char &a, char &b, char &c, char &d, char &e, char &f, char &g) {
  RC(a), RC(b), RC(c), RC(d), RC(e), RC(f), RC(g);
  return a;
}
inline DB &RF(DB &a, DB &b) {
  RF(a), RF(b);
  return a;
}
inline DB &RF(DB &a, DB &b, DB &c) {
  RF(a), RF(b), RF(c);
  return a;
}
inline DB &RF(DB &a, DB &b, DB &c, DB &d) {
  RF(a), RF(b), RF(c), RF(d);
  return a;
}
inline DB &RF(DB &a, DB &b, DB &c, DB &d, DB &e) {
  RF(a), RF(b), RF(c), RF(d), RF(e);
  return a;
}
inline DB &RF(DB &a, DB &b, DB &c, DB &d, DB &e, DB &f) {
  RF(a), RF(b), RF(c), RF(d), RF(e), RF(f);
  return a;
}
inline DB &RF(DB &a, DB &b, DB &c, DB &d, DB &e, DB &f, DB &g) {
  RF(a), RF(b), RF(c), RF(d), RF(e), RF(f), RF(g);
  return a;
}
inline void RS(char *s1, char *s2) { RS(s1), RS(s2); }
inline void RS(char *s1, char *s2, char *s3) { RS(s1), RS(s2), RS(s3); }
template <class T0, class T1> inline T0 &RDD(T0 &a, T1 &b) {
  RDD(a), RDD(b);
  return a;
}
template <class T0, class T1, class T2> inline T1 &RDD(T0 &a, T1 &b, T2 &c) {
  RDD(a), RDD(b), RDD(c);
  return a;
}

template <class T> inline void RST(T &A) { memset(A, 0, sizeof(A)); }
template <class T> inline void FLC(T &A, int x) { memset(A, x, sizeof(A)); }
template <class T> inline void CLR(T &A) { A.clear(); }

template <class T0, class T1> inline void RST(T0 &A0, T1 &A1) {
  RST(A0), RST(A1);
}
template <class T0, class T1, class T2>
inline void RST(T0 &A0, T1 &A1, T2 &A2) {
  RST(A0), RST(A1), RST(A2);
}
template <class T0, class T1, class T2, class T3>
inline void RST(T0 &A0, T1 &A1, T2 &A2, T3 &A3) {
  RST(A0), RST(A1), RST(A2), RST(A3);
}
template <class T0, class T1, class T2, class T3, class T4>
inline void RST(T0 &A0, T1 &A1, T2 &A2, T3 &A3, T4 &A4) {
  RST(A0), RST(A1), RST(A2), RST(A3), RST(A4);
}
template <class T0, class T1, class T2, class T3, class T4, class T5>
inline void RST(T0 &A0, T1 &A1, T2 &A2, T3 &A3, T4 &A4, T5 &A5) {
  RST(A0), RST(A1), RST(A2), RST(A3), RST(A4), RST(A5);
}
template <class T0, class T1, class T2, class T3, class T4, class T5, class T6>
inline void RST(T0 &A0, T1 &A1, T2 &A2, T3 &A3, T4 &A4, T5 &A5, T6 &A6) {
  RST(A0), RST(A1), RST(A2), RST(A3), RST(A4), RST(A5), RST(A6);
}
template <class T0, class T1> inline void FLC(T0 &A0, T1 &A1, int x) {
  FLC(A0, x), FLC(A1, x);
}
template <class T0, class T1, class T2>
inline void FLC(T0 &A0, T1 &A1, T2 &A2, int x) {
  FLC(A0, x), FLC(A1, x), FLC(A2, x);
}
template <class T0, class T1, class T2, class T3>
inline void FLC(T0 &A0, T1 &A1, T2 &A2, T3 &A3, int x) {
  FLC(A0, x), FLC(A1, x), FLC(A2, x), FLC(A3, x);
}
template <class T0, class T1, class T2, class T3, class T4>
inline void FLC(T0 &A0, T1 &A1, T2 &A2, T3 &A3, T4 &A4, int x) {
  FLC(A0, x), FLC(A1, x), FLC(A2, x), FLC(A3, x), FLC(A4, x);
}
template <class T0, class T1, class T2, class T3, class T4, class T5>
inline void FLC(T0 &A0, T1 &A1, T2 &A2, T3 &A3, T4 &A4, T5 &A5, int x) {
  FLC(A0, x), FLC(A1, x), FLC(A2, x), FLC(A3, x), FLC(A4, x), FLC(A5, x);
}
template <class T0, class T1, class T2, class T3, class T4, class T5, class T6>
inline void FLC(T0 &A0, T1 &A1, T2 &A2, T3 &A3, T4 &A4, T5 &A5, T6 &A6, int x) {
  FLC(A0, x), FLC(A1, x), FLC(A2, x), FLC(A3, x), FLC(A4, x), FLC(A5, x),
      FLC(A6, x);
}
template <class T> inline void CLR(priority_queue<T, vector<T>, less<T>> &Q) {
  while (!Q.empty())
    Q.pop();
}
template <class T>
inline void CLR(priority_queue<T, vector<T>, greater<T>> &Q) {
  while (!Q.empty())
    Q.pop();
}
template <class T> inline void CLR(stack<T> &S) {
  while (!S.empty())
    S.pop();
}
template <class T> inline void CLR(queue<T> &Q) {
  while (!Q.empty())
    Q.pop();
}

template <class T0, class T1> inline void CLR(T0 &A0, T1 &A1) {
  CLR(A0), CLR(A1);
}
template <class T0, class T1, class T2>
inline void CLR(T0 &A0, T1 &A1, T2 &A2) {
  CLR(A0), CLR(A1), CLR(A2);
}
template <class T0, class T1, class T2, class T3>
inline void CLR(T0 &A0, T1 &A1, T2 &A2, T3 &A3) {
  CLR(A0), CLR(A1), CLR(A2), CLR(A3);
}
template <class T0, class T1, class T2, class T3, class T4>
inline void CLR(T0 &A0, T1 &A1, T2 &A2, T3 &A3, T4 &A4) {
  CLR(A0), CLR(A1), CLR(A2), CLR(A3), CLR(A4);
}
template <class T0, class T1, class T2, class T3, class T4, class T5>
inline void CLR(T0 &A0, T1 &A1, T2 &A2, T3 &A3, T4 &A4, T5 &A5) {
  CLR(A0), CLR(A1), CLR(A2), CLR(A3), CLR(A4), CLR(A5);
}
template <class T0, class T1, class T2, class T3, class T4, class T5, class T6>
inline void CLR(T0 &A0, T1 &A1, T2 &A2, T3 &A3, T4 &A4, T5 &A5, T6 &A6) {
  CLR(A0), CLR(A1), CLR(A2), CLR(A3), CLR(A4), CLR(A5), CLR(A6);
}
template <class T> inline void CLR(T &A, int n) { REP(i, n) CLR(A[i]); }

template <class T> inline bool EPT(T &a) { return a.empty(); }
template <class T> inline T &SRT(T &A) {
  sort(ALL(A));
  return A;
}
template <class T, class C> inline T &SRT(T &A, C cmp) {
  sort(ALL(A), cmp);
  return A;
}
template <class T> inline T &RVS(T &A) {
  reverse(ALL(A));
  return A;
}
template <class T> inline T &UNQQ(T &A) {
  A.resize(unique(ALL(A)) - A.begin());
  return A;
}
template <class T> inline T &UNQ(T &A) {
  SRT(A);
  return UNQQ(A);
}
template <class T, class C> inline T &UNQ(T &A, C cmp) {
  SRT(A, cmp);
  return UNQQ(A);
}

//}

/** Constant List .. **/ //{

const int MOD = int(1e9) + 7;
const int INF = 0x3f3f3f3f;
const LL INFF = 0x3f3f3f3f3f3f3f3fLL;
const DB EPS = 1e-9;
const DB OO = 1e20;
const DB PI = acos(-1.0); // M_PI;

const int dx[] = {-1, 0, 1, 0};
const int dy[] = {0, 1, 0, -1};

//}

/** Add On .. **/ //{
// <<= '0. Nichi Joo ., //{

template <class T> inline bool checkMin(T &a, const T b) {
  return b < a ? a = b, 1 : 0;
}
template <class T> inline bool checkMax(T &a, const T b) {
  return a < b ? a = b, 1 : 0;
}
template <class T, class C> inline bool checkUpd(T &a, const T b, C c) {
  return c(b, a) ? a = b, 1 : 0;
}
template <class T> inline T min(T a, T b, T c) { return min(min(a, b), c); }
template <class T> inline T max(T a, T b, T c) { return max(max(a, b), c); }
template <class T> inline T min(T a, T b, T c, T d) {
  return min(min(a, b), min(c, d));
}
template <class T> inline T max(T a, T b, T c, T d) {
  return max(max(a, b), max(c, d));
}
template <class T> inline T min(T a, T b, T c, T d, T e) {
  return min(min(min(a, b), min(c, d)), e);
}
template <class T> inline T max(T a, T b, T c, T d, T e) {
  return max(max(max(a, b), max(c, d)), e);
}
template <class T> inline T sqr(T a) { return a * a; }
template <class T> inline T cub(T a) { return a * a * a; }
template <class T> inline T ceil(T x, T y) { return (x - 1) / y + 1; }
template <class T> T abs(T x) { return x > 0 ? x : -x; }
inline int sgn(DB x) { return x < -EPS ? -1 : x > EPS; }
inline int sgn(DB x, DB y) { return sgn(x - y); }

inline DB cos(DB a, DB b, DB c) {
  return (sqr(a) + sqr(b) - sqr(c)) / (2 * a * b);
}
inline DB cot(DB x) { return 1. / tan(x); };
inline DB sec(DB x) { return 1. / cos(x); };
inline DB csc(DB x) { return 1. / sin(x); };

//}
// <<= '1. Bitwise Operation ., //{
namespace BO {

inline bool _1(int x, int i) { return bool(x & 1 << i); }
inline bool _1(LL x, int i) { return bool(x & 1LL << i); }
inline LL _1(int i) { return 1LL << i; }
inline LL _U(int i) { return _1(i) - 1; };

inline int reverse_bits(int x) {
  x = ((x >> 1) & 0x55555555) | ((x << 1) & 0xaaaaaaaa);
  x = ((x >> 2) & 0x33333333) | ((x << 2) & 0xcccccccc);
  x = ((x >> 4) & 0x0f0f0f0f) | ((x << 4) & 0xf0f0f0f0);
  x = ((x >> 8) & 0x00ff00ff) | ((x << 8) & 0xff00ff00);
  x = ((x >> 16) & 0x0000ffff) | ((x << 16) & 0xffff0000);
  return x;
}

inline LL reverse_bits(LL x) {
  x = ((x >> 1) & 0x5555555555555555LL) | ((x << 1) & 0xaaaaaaaaaaaaaaaaLL);
  x = ((x >> 2) & 0x3333333333333333LL) | ((x << 2) & 0xccccccccccccccccLL);
  x = ((x >> 4) & 0x0f0f0f0f0f0f0f0fLL) | ((x << 4) & 0xf0f0f0f0f0f0f0f0LL);
  x = ((x >> 8) & 0x00ff00ff00ff00ffLL) | ((x << 8) & 0xff00ff00ff00ff00LL);
  x = ((x >> 16) & 0x0000ffff0000ffffLL) | ((x << 16) & 0xffff0000ffff0000LL);
  x = ((x >> 32) & 0x00000000ffffffffLL) | ((x << 32) & 0xffffffff00000000LL);
  return x;
}

template <class T> inline bool odd(T x) { return x & 1; }
template <class T> inline bool even(T x) { return !odd(x); }
template <class T> inline T low_bit(T x) { return x & -x; }
template <class T> inline T high_bit(T x) {
  T p = low_bit(x);
  while (p != x)
    x -= p, p = low_bit(x);
  return p;
}
template <class T> inline T cover_bit(T x) {
  T p = 1;
  while (p < x)
    p <<= 1;
  return p;
}
template <class T> inline int cover_idx(T x) {
  int p = 0;
  while (_1(p) < x)
    ++p;
  return p;
}

inline int clz(int x) { return __builtin_clz(x); }
inline int clz(LL x) { return __builtin_clzll(x); }
inline int ctz(int x) { return __builtin_ctz(x); }
inline int ctz(LL x) { return __builtin_ctzll(x); }
inline int lg2(int x) { return !x ? -1 : 31 - clz(x); }
inline int lg2(LL x) { return !x ? -1 : 63 - clz(x); }
inline int low_idx(int x) { return !x ? -1 : ctz(x); }
inline int low_idx(LL x) { return !x ? -1 : ctz(x); }
inline int high_idx(int x) { return lg2(x); }
inline int high_idx(LL x) { return lg2(x); }
inline int parity(int x) { return __builtin_parity(x); }
inline int parity(LL x) { return __builtin_parityll(x); }
inline int count_bits(int x) { return __builtin_popcount(x); }
inline int count_bits(LL x) { return __builtin_popcountll(x); }

} // namespace BO
using namespace BO; //}

// <<= '2. Number Theory .,//{
namespace NT {
#define gcd __gcd
inline LL lcm(LL a, LL b) { return a * b / gcd(a, b); }

inline void INC(int &a, int b) {
  a += b;
  if (a >= MOD)
    a -= MOD;
}
inline int sum(int a, int b) {
  a += b;
  if (a >= MOD)
    a -= MOD;
  return a;
}

/* 模数两倍刚好超 int 时。
 inline int sum(uint a, int b){a += b; a %= MOD;if (a < 0) a += MOD; return a;}
 inline void INC(int &a, int b){a = sum(a, b);}
 */

inline void DEC(int &a, int b) {
  a -= b;
  if (a < 0)
    a += MOD;
}
inline int dff(int a, int b) {
  a -= b;
  if (a < 0)
    a += MOD;
  return a;
}
inline void MUL(int &a, int b) { a = (LL)a * b % MOD; }
// inline int pdt(int a, int b){return (LL)a * b % MOD;}
inline int pdt(int x, int y) {
  int ret;
  __asm__ __volatile__("\tmull %%ebx\n\tdivl %%ecx\n"
                       : "=d"(ret)
                       : "a"(x), "b"(y), "c"(MOD));
  return ret;
}

inline int gcd(int m, int n, int &x, int &y) {

  x = 1, y = 0;
  int xx = 0, yy = 1, q;

  while (1) {
    q = m / n, m %= n;
    if (!m) {
      x = xx, y = yy;
      return n;
    }
    DEC(x, pdt(q, xx)), DEC(y, pdt(q, yy));
    q = n / m, n %= m;
    if (!n)
      return m;
    DEC(xx, pdt(q, x)), DEC(yy, pdt(q, y));
  }
}

inline int sum(int a, int b, int c) { return sum(a, sum(b, c)); }
inline int sum(int a, int b, int c, int d) { return sum(sum(a, b), sum(c, d)); }
inline int pdt(int a, int b, int c) { return pdt(a, pdt(b, c)); }
inline int pdt(int a, int b, int c, int d) { return pdt(pdt(a, b), pdt(c, d)); }

inline int pow(int a, LL b) {
  int c(1);
  while (b) {
    if (b & 1)
      MUL(c, a);
    MUL(a, a), b >>= 1;
  }
  return c;
}

template <class T> inline T pow(T a, LL b) {
  T c(1);
  while (b) {
    if (b & 1)
      c *= a;
    a *= a, b >>= 1;
  }
  return c;
}

template <class T> inline T pow(T a, int b) { return pow(a, (LL)b); }

inline int _I(int b) {
  int a = MOD, x1 = 0, x2 = 1, q;
  while (1) {
    q = a / b, a %= b;
    if (!a)
      return x2;
    DEC(x1, pdt(q, x2));

    q = b / a, b %= a;
    if (!b)
      return x1;
    DEC(x2, pdt(q, x1));
  }
}

inline void DIV(int &a, int b) { MUL(a, _I(b)); }
inline int qtt(int a, int b) { return pdt(a, _I(b)); }

struct Int {
  int val;

  operator int() const { return val; }

  Int(int _val = 0) : val(_val) {
    val %= MOD;
    if (val < 0)
      val += MOD;
  }
  Int(LL _val) : val(_val) {
    _val %= MOD;
    if (_val < 0)
      _val += MOD;
    val = _val;
  }

  Int &operator+=(const int &rhs) {
    INC(val, rhs);
    rTs;
  }
  Int operator+(const int &rhs) const { return sum(val, rhs); }
  Int &operator-=(const int &rhs) {
    DEC(val, rhs);
    rTs;
  }
  Int operator-(const int &rhs) const { return dff(val, rhs); }
  Int &operator*=(const int &rhs) {
    MUL(val, rhs);
    rTs;
  }
  Int operator*(const int &rhs) const { return pdt(val, rhs); }
  Int &operator/=(const int &rhs) {
    DIV(val, rhs);
    rTs;
  }
  Int operator/(const int &rhs) const { return qtt(val, rhs); }
  Int operator-() const { return MOD - *this; }
};

} // namespace NT
using namespace NT; //}

//}

/** I/O Accelerator Interface .. **/ //{
#define g (c = getchar())
#define d isdigit(g)
#define p x = x * 10 + c - '0'
#define n x = x * 10 + '0' - c
#define pp l /= 10, p
#define nn l /= 10, n
template <class T> inline T &RD(T &x) {
  char c;
  while (!d)
    ;
  x = c - '0';
  while (d)
    p;
  return x;
}
template <class T> inline T &RDD(T &x) {
  char c;
  while (g, c != '-' && !isdigit(c))
    ;
  if (c == '-') {
    x = '0' - g;
    while (d)
      n;
  } else {
    x = c - '0';
    while (d)
      p;
  }
  return x;
}
inline DB &RF(DB &x) {
  // scanf("%lf", &x);
  char c;
  while (g, c != '-' && c != '.' && !isdigit(c))
    ;
  if (c == '-')
    if (g == '.') {
      x = 0;
      DB l = 1;
      while (d)
        nn;
      x *= l;
    } else {
      x = '0' - c;
      while (d)
        n;
      if (c == '.') {
        DB l = 1;
        while (d)
          nn;
        x *= l;
      }
    }
  else if (c == '.') {
    x = 0;
    DB l = 1;
    while (d)
      pp;
    x *= l;
  } else {
    x = c - '0';
    while (d)
      p;
    if (c == '.') {
      DB l = 1;
      while (d)
        pp;
      x *= l;
    }
  }
  return x;
}
#undef nn
#undef pp
#undef n
#undef p
#undef d
#undef g
inline char *RS(char *s) {
  // gets(s);
  scanf("%s", s);
  return s;
}

LL last_ans;
int Case;
template <class T> inline void OT(const T &x) {
  // printf("Case #%d: ", ++Case);
  // printf("%lld\n", x);
  // printf("%I64d\n", x);
  // printf("%.9f\n", x);
  // printf("%d\n", x);
  cout << x << endl;
  // last_ans = x;
}

//}/*
//..................................................................................................................................
//*/

const int N = int(1e5) + 9;
int P[N], n;

int main() {

#ifndef ONLINE_JUDGE
  // freopen("/users/minakokojima/ACM-Training/Workspace/in.txt", "r", stdin);
  // freopen("/users/minakokojima/ACM-Training/Workspace/out.txt", "w", stdout);
#endif

  RD(n);
  REP_1(i, n) RD(P[i]);
  int z = 0;
  REP_1(i, n) if (P[i] == i) {
    ++z;
    if (i != n)
      swap(P[i], P[i + 1]);
    else
      swap(P[i], P[i - 1]);
  }
  cout << z << endl;
}