#define _USE_MATH_DEFINES
#include <bits/stdc++.h>

using namespace std;

#define dprint(Exp,...) if(Exp){fprintf(stderr, __VA_ARGS__);}
#define printe(...) fprintf(stderr, __VA_ARGS__);
#define PrtExp(_Exp)  cerr<< #_Exp <<" = "<< (_Exp)
#define PrtExpN(_Exp)  cerr<< #_Exp <<" = "<< (_Exp) <<"\n"

#define SINT(n) scanf("%d",&n)
#define SINT2(n,m) scanf("%d %d",&n,&m)
#define SINT3(n,m,o) scanf("%d %d %d",&n,&m,&o)
#define SINT4(n,m,o,p) scanf("%d %d %d %d",&n,&m,&o,&p)
#define SINT5(n,m,o,p,q) scanf("%d %d %d %d %d",&n,&m,&o,&p,&q)
#define SLL(n) scanf("%lld",&n)
#define SLL2(n,m) scanf("%lld %lld",&n,&m)
#define SLL3(n,m,o) scanf("%lld %lld %lld",&n,&m,&o)
#define SST(s) scanf("%s",s)
#define SCH(c) scanf("%c",&c)

#define GC() getchar()

#define PINT(n) printf("%d",(int)(n))
#define PINT2(n,m) printf("%d %d",(int)(n),(int)(m))
#define PINT3(n,m,l) printf("%d %d %d",(int)(n),(int)(m),(int)(l))
#define PLL(n) printf("%lld",(long long)(n))
#define PST(s) printf("%s",(s))
#define PCH(s) printf("%c",(s))

#define PINTN(n) printf("%d\n",(int)(n))
#define PINT2N(n,m) printf("%d %d\n",(int)(n),(int)(m))
#define PINT3N(n,m,l) printf("%d %d %d\n",(int)(n),(int)(m),(int)(l))
#define PLLN(n) printf("%lld\n",(long long)(n))
#define PSTN(s) printf("%s\n",(s))
#define PCHN(s) printf("%c\n",(s))

#define PSP() printf(" ")
#define PN() printf("\n")

#define PC(c) putchar(c)
#define CSP (' ')
#define SN ("\n")

#define rep(i,a) for(int i=0;i<a;i++)
#define reP(i,a) for(int i=0;i<=a;i++)
#define Rep(i,a) for(int i=a-1;i>=0;i--)
#define ReP(i,a) for(int i=a;i>=0;i--)

#define rEp(i,a) for(i=0;i<a;i++)
#define rEP(i,a) for(i=0;i<=a;i++)
#define REp(i,a) for(i=a-1;i>=0;i--)
#define REP(i,a) for(i=a;i>=0;i--)

#define repft(i,a,b) for(int i=a;i<b;i++)
#define repfT(i,a,b) for(int i=a;i<=b;i++)
#define Repft(i,a,b) for(int i=a-1;i>=b;i--)
#define RepfT(i,a,b) for(int i=a;i>=b;i--)

#define foreach(a,it) for(auto it = a.begin(); it != a.end(); ++it)

#define FILL(a,v) fill(begin(a),end(a), v)
#define FILL0(a) memset(a,0,sizeof(a))
#define FILL1(a) memset(a,-1,sizeof(a))

typedef long long ll;
typedef unsigned long long ull;
typedef pair<int, int> Pi;
typedef pair<ll, ll>   Pll;


const int INF = 0x2aaaaaaa; // 715,827,882
const ll INFLL = 0x1f1f1f1f1f1f1f1fLL;//2,242,545,357,980,376,863

template <class A, class B> inline ostream& operator<<(ostream& st, const pair<A, B>& P) { return st << "(" << P.first << "," << P.second << ")"; };
template <class A, class B> inline pair<A, B> operator+(const pair<A, B>& P, const pair<A, B>& Q) { return pair<A, B>(P.first + Q.first, P.second + Q.second); };
template <class A, class B> inline pair<A, B> operator-(const pair<A, B>& P, const pair<A, B>& Q) { return pair<A, B>(P.first - Q.first, P.second - Q.second); };


#define fs first
#define sc second



int p[100005];
int main() {
	int n;
	cin >> n;
	ll ret = 0;
	rep(i, n) {
		cin >> p[i]; --p[i];
	}
	rep(i, n) {
		if (p[i] == i) {
			swap(p[i], p[i + 1]);
			ret++;
		}
	}
	cout << ret << endl;
}

/*


1 . . . . 6
.         .
1 3 4 5 2 6



1 2 . 4 5 . . 8 . 10 11
1 2 9 4 5 3 6 8 7 10 11

11
1 2 9 4 5 3 6 8 7 10 11
. .   . .     .   . .

.. ..   . ..
1 2 1 3 2 1  -> 1+1+1  +1



1 4 3 5 2
.   .

1 2 4 9 5 8 7 3 6
. .     .   .   

8
1 2 3 5 6 7 8 4
. . .
1 2 3 5 6 7 8 4
2 1 3 5 6 7 8 4
2 3 1 5 6 7 8 4


8
1 2 5 4 6 7 8 3
. .   .
1 2 5 4 6 7 8 3
2 1 5 4 6 7 8 3
2 1 4 5 6 7 8 3


1 2   -> 1 +1
2 1   -> 1 +1

.. ..
1 2 1  -> 1+1 +1



*/

Measured memory_bytes: 640