Problem p02691 (C++)

Buggy submission (status: Runtime Error):
#include <algorithm>
#include <cmath>
#include <cstdio>

#ifndef LX_DEBUG
// #define LX_DEBUG
#endif

#if defined(__unix__) && !defined(LX_DEBUG) && !defined(LX_LOCAL)
#define USE_MMAP 1
#include <fcntl.h>
#include <sys/mman.h>
#include <sys/stat.h>
#include <sys/types.h>
#include <unistd.h>
#else
#define USE_MMAP 0
#endif

using LL = long long;
using ULL = unsigned long long;
#ifdef __SIZEOF_INT128__
using LLL = __int128;
using ULLL = unsigned __int128;
#else
using LLL = long long;
using ULLL = unsigned long long;
#endif

namespace std {
#define def(type)                                                              \
  void swap(type &x, type &y) { x ^= y ^= x ^= y; }
def(char);
def(signed char);
def(unsigned char);
def(short);
def(unsigned short);
def(int);
def(unsigned int);
def(LL);
def(ULL);
#ifdef __SIZEOF_INT128__
def(LLL);
def(ULLL);
#endif
#undef def
}; // namespace std

#ifdef LX_LOCAL
#include <ctime>
class Time {
public:
  clock_t begin;
  Time() { begin = clock(); }
  ~Time() {
    double t = (clock() - begin) * 1000.0 / static_cast<double>(CLOCKS_PER_SEC);
    fprintf(stderr, "Time used = ");
    if (t >= 60000)
      fprintf(stderr, "%.2lfmin\n", t / 60000.0);
    else if (t >= 1000)
      fprintf(stderr, "%.2lfs\n", t / 1000.0);
    else
      fprintf(stderr, "%.0lfms\n", t);
  }
} timeout;
#endif

using std::swap;
#if __cplusplus >= 201402L
template <typename T, typename P>
inline constexpr auto max(const T &x, const P &y) {
  return x < y ? y : x;
}
template <typename T, typename P>
inline constexpr auto min(const T &x, const P &y) {
  return x < y ? x : y;
}
template <typename T, typename... Args>
inline constexpr auto max(const T &x, const Args &...args) {
  return max(x, max(args...));
}
template <typename T, typename... Args>
inline constexpr auto min(const T &x, const Args &...args) {
  return min(x, min(args...));
}
#else
template <typename T, typename P>
inline constexpr auto max(const T &x, const P &y) -> decltype(x < y ? y : x) {
  return x < y ? y : x;
}
template <typename T, typename P>
inline constexpr auto min(const T &x, const P &y) -> decltype(x < y ? x : y) {
  return x < y ? x : y;
}
template <typename T, typename... Args>
inline constexpr auto max(const T &x, const Args &...args)
    -> decltype(max(x, max(args...))) {
  return max(x, max(args...));
}
template <typename T, typename... Args>
inline constexpr auto min(const T &x, const Args &...args)
    -> decltype(min(x, min(args...))) {
  return min(x, min(args...));
}
#endif
template <typename T> inline constexpr T max(const T &x) { return x; }
template <typename T> inline constexpr T min(const T &x) { return x; }
template <typename T, typename... Args>
inline void chkmax(T &d, const Args &...args) {
  d = max(d, args...);
}
template <typename T, typename... Args>
inline void chkmin(T &d, const Args &...args) {
  d = min(d, args...);
}

#define lc (o << 1)
#define rc (o << 1 | 1)
#define lowbit(x) ((x) & (-(x)))
#define all(x) x.begin(), x.end()
#define SZ(x) int(x.size())

#pragma region IO
constexpr size_t bufSize = 1 << 20;

class In {
private:
  FILE *inFile = nullptr;
#if USE_MMAP
  struct stat st;
  char *ptr;
  int fd;
  size_t pos;
#elif !defined(LX_DEBUG)
  char buf[bufSize], *p1, *p2;
#endif
public:
#ifdef LX_DEBUG
  inline int getch() { return fgetc(inFile); }
  inline void putback(char c) { ungetc(c, inFile); }
  inline void input(FILE *f) { inFile = f; }
  inline void input(const char *str) { inFile = fopen(str, "rb"); }
#elif USE_MMAP
  inline int getch() { return *(ptr + pos) ? *(ptr + (pos++)) : EOF; }
  inline void putback(char c) { pos--; }
  inline void input(FILE *f) {
    if ((inFile = f))
      fd = fileno(inFile), fstat(fd, &st),
      ptr = (char *)mmap(0, st.st_size, PROT_READ, MAP_PRIVATE, fd, 0), pos = 0;
  }
  inline void input(const char *str) {
    fd = open(str, O_RDONLY), fstat(fd, &st),
    ptr = (char *)mmap(0, st.st_size, PROT_READ, MAP_PRIVATE, fd, 0), pos = 0;
  }
#else
  inline int getch() {
    return (p1 == p2 ? (p2 = (p1 = buf) + fread(buf, 1, bufSize, inFile)) : 0),
           (p1 == p2) ? EOF : *p1++;
  }
  inline void putback(char c) { *(--p1) = c; }
  inline void input(FILE *f) { inFile = f, p1 = p2 = buf; }
  inline void input(const char *str) {
    inFile = fopen(str, "rb"), p1 = p2 = buf;
  }
#endif
};
class Out {
private:
  FILE *outFile = nullptr;
#ifndef LX_DEBUG
  char pbuf[bufSize], *pp;
#endif
public:
#ifdef LX_DEBUG
  inline void flush() { outFile ? fflush(outFile) : 0; }
  inline void putch(const char c) { fputc(c, outFile); }
#else
  inline void flush() {
    (outFile ? fwrite(pbuf, 1, pp - pbuf, outFile), fflush(outFile) : 0),
        pp = pbuf;
  }
  inline void putch(const char c) {
    ((pp - pbuf == bufSize) ? fwrite(pbuf, 1, bufSize, outFile), pp = pbuf : 0),
        *pp++ = c;
  }
#endif
  inline void output(const char *str) { flush(), outFile = fopen(str, "wb"); }
  inline void output(FILE *f) { flush(), outFile = f; }
};
class IO : public In, public Out {
private:
  long double eps = 1e-8L;
  LLL pow10 = 1000000;
  size_t precision = 6;

public:
  IO(FILE *in = nullptr, FILE *out = nullptr);
  ~IO();
  inline void flush();
  inline static constexpr bool blank(char ch);
  template <typename T, typename... Args> bool read(T &x, Args &...args);
  template <typename T>
  typename std::enable_if<
      (std::is_signed<T>::value && std::is_integral<T>::value) ||
          std::is_same<typename std::remove_cv<T>::type, LLL>::value,
      bool>::type
  read(T &x);
  template <typename T>
  typename std::enable_if<
      (std::is_unsigned<T>::value && std::is_integral<T>::value) ||
          std::is_same<typename std::remove_cv<T>::type, ULLL>::value,
      bool>::type
  read(T &x);
  template <typename T>
  typename std::enable_if<std::is_floating_point<T>::value, bool>::type
  read(T &x);
  template <typename T>
  typename std::enable_if<
      std::is_integral<T>::value || std::is_floating_point<T>::value ||
          std::is_same<typename std::remove_cv<T>::type, LLL>::value ||
          std::is_same<typename std::remove_cv<T>, ULLL>::value,
      T>::type
  read();
  bool read(char &ch);
  bool read(char *s);
  bool readline(char *s);
  inline void setprecision(size_t n = 6u);
  template <typename T, typename... Args>
  void write(const T &x, const Args &...args);
  inline void write() const {}
  template <typename T>
  typename std::enable_if<(std::is_signed<T>::value &&
                           std::is_integral<T>::value) ||
                              std::is_same<T, LLL>::value,
                          void>::type
  write(T x);
  template <typename T>
  typename std::enable_if<(std::is_unsigned<T>::value &&
                           std::is_integral<T>::value) ||
                              std::is_same<T, ULLL>::value,
                          void>::type
  write(T x);
  inline void write(char c);
  template <typename T>
  typename std::enable_if<std::is_floating_point<T>::value, void>::type
  write(T x);
  inline void write(bool x);
  void write(char *s);
  void write(const char *s);
  template <typename... Args> void writeln(Args... x);
} io(stdin, stdout), err(nullptr, stderr);
template <typename... Args> inline void writeln(Args... x) {
  io.write(x...), io.putch('\n');
}
#define dbg(x) err.write(#x " = "), err.writeln(x)
#pragma endregion IO
#include <map>
const int maxn = 100005;

int A[maxn];
int main() {
  int n;
  io.read(n);
  for (int i = 1; i <= n; i++)
    io.read(A[i]);
  std::map<int, int> mp, mp2;
  for (int i = 1; i <= n; i++)
    mp[i - A[i]]++;
  LL ans = 0;
  for (int i = 1; i <= n; i++)
    ans += mp[A[i] + i];
  writeln(ans);
  return 0;
}

#define isdigit(x) (x >= '0' && x <= '9')
IO::IO(FILE *in, FILE *out) { input(in), output(out); }
IO::~IO() { flush(); }
inline void IO::flush() { Out::flush(); }
inline constexpr bool IO::blank(char ch) {
  return ch == ' ' || ch == '\n' || ch == '\r' || ch == '\t';
}
template <typename T, typename... Args> bool IO::read(T &x, Args &...args) {
  return read(x) && (sizeof...(args) ? read(args...) : true);
}
template <typename T>
typename std::enable_if<
    (std::is_signed<T>::value && std::is_integral<T>::value) ||
        std::is_same<typename std::remove_cv<T>::type, LLL>::value,
    bool>::type
IO::read(T &x) {
  x = 0;
  bool sign = false;
  int ch = getch();
  while (!isdigit(ch) && ~ch)
    sign &= (ch == '-'), ch = getch();
  if (!(~ch))
    return false;
  while (isdigit(ch))
    x = (x << 1) + (x << 3) + (ch ^ '0'), ch = getch();
  if (~ch)
    putback(ch);
  x = sign ? (~x + 1) : x;
  return true;
}
template <typename T>
typename std::enable_if<
    (std::is_unsigned<T>::value && std::is_integral<T>::value) ||
        std::is_same<typename std::remove_cv<T>::type, ULLL>::value,
    bool>::type
IO::read(T &x) {
  x = 0;
  int ch = getch();
  while (!isdigit(ch) && ~ch)
    ch = getch();
  if (!(~ch))
    return false;
  while (isdigit(ch))
    x = (x << 1) + (x << 3) + (ch ^ '0'), ch = getch();
  if (~ch)
    putback(ch);
  return true;
}
template <typename T>
typename std::enable_if<std::is_floating_point<T>::value, bool>::type
IO::read(T &x) {
  x = 0;
  T tmp = 1;
  bool sign = false;
  int ch = getch();
  while (!isdigit(ch) && ~ch)
    sign &= (ch == '-'), ch = getch();
  if (!(~ch))
    return false;
  while (isdigit(ch))
    x = x * 10 + (ch ^ '0'), ch = getch();
  if (ch == '.')
    for (ch = getch(); isdigit(ch); ch = getch())
      x += (tmp /= 10.0) * (ch ^ '0');
  if (~ch)
    putback(ch);
  x = sign ? (-x) : x;
  return true;
}
template <typename T>
typename std::enable_if<
    std::is_integral<T>::value || std::is_floating_point<T>::value ||
        std::is_same<typename std::remove_cv<T>::type, LLL>::value ||
        std::is_same<typename std::remove_cv<T>, ULLL>::value,
    T>::type
IO::read() {
  typename std::remove_cv<T>::type x;
  read(x);
  return x;
}
bool IO::read(char &ch) {
  do
    ch = getch();
  while (blank(ch) && ~ch);
  return ~ch;
}
bool IO::read(char *s) {
  int ch = getch();
  while (blank(ch))
    ch = getch();
  if (!(~ch))
    return false;
  while (!blank(ch) && ~ch)
    *s++ = ch, ch = getch();
  *s = 0;
  if (~ch)
    putback(ch);
  return true;
}
bool IO::readline(char *s) {
  int ch = getch();
  while (blank(ch) && (ch ^ '\n'))
    ch = getch();
  if (!(~ch))
    return false;
  while ((ch ^ '\n') && ~ch)
    *s++ = ch, ch = getch();
  *s = 0;
  if (~ch)
    putback(ch);
  return true;
}
inline void IO::setprecision(size_t n) {
  precision = n;
  eps = powl(10.0L, -precision - 2);
  pow10 = powl(10.0L, precision) + eps;
}
template <typename T, typename... Args>
void IO::write(const T &x, const Args &...args) {
  write(x);
  if (sizeof...(args))
    write(args...);
}
template <typename T>
typename std::enable_if<(std::is_signed<T>::value &&
                         std::is_integral<T>::value) ||
                            std::is_same<T, LLL>::value,
                        void>::type
IO::write(T x) {
  if (x < 0)
    x = ~x + 1, putch('-');
  static int sta[40], top = 0;
  do
    sta[top++] = x % 10, x /= 10;
  while (x);
  while (top)
    putch(sta[--top] ^ '0');
}
template <typename T>
typename std::enable_if<(std::is_unsigned<T>::value &&
                         std::is_integral<T>::value) ||
                            std::is_same<T, ULLL>::value,
                        void>::type
IO::write(T x) {
  static int sta[40], top = 0;
  do
    sta[top++] = x % 10, x /= 10;
  while (x);
  while (top)
    putch(sta[--top] ^ '0');
}
inline void IO::write(bool x) { putch(x ^ 48); }
inline void IO::write(char c) { putch(c); }
template <typename T>
typename std::enable_if<std::is_floating_point<T>::value>::type IO::write(T x) {
  if (x == 0) {
    putch('0'), putch('.');
    for (int i = 1; i <= precision; i++)
      putch('0');
    return;
  }
  if (x < 0)
    putch('-'), x = -x;
  T res = (LLL)(x * pow10 + 0.5) / (pow10 * 1.0);
  LLL y = LLL(res * pow10 + eps) % pow10;
  write(LLL(res + eps));
  if (precision) {
    putch('.');
    static int sta[100], p = 0;
    while (p < precision)
      sta[++p] = y % 10, y /= 10;
    for (int i = p; i >= 1; i--)
      putch(sta[i] ^ 48);
  }
}
void IO::write(char *s) {
  while (*s)
    putch(*s++);
}
void IO::write(const char *s) {
  while (*s)
    putch(*s++);
}
template <typename... Args> void IO::writeln(Args... x) {
  write(x...), putch('\n');
}
#undef isdigit

Fixed submission:
#include <algorithm>
#include <cmath>
#include <cstdio>

#ifndef LX_DEBUG
// #define LX_DEBUG
#endif

#if defined(__unix__) && !defined(LX_DEBUG) && !defined(LX_LOCAL)
#define USE_MMAP 1
#include <fcntl.h>
#include <sys/mman.h>
#include <sys/stat.h>
#include <sys/types.h>
#include <unistd.h>
#else
#define USE_MMAP 0
#endif

using LL = long long;
using ULL = unsigned long long;
#ifdef __SIZEOF_INT128__
using LLL = __int128;
using ULLL = unsigned __int128;
#else
using LLL = long long;
using ULLL = unsigned long long;
#endif

namespace std {
#define def(type)                                                              \
  void swap(type &x, type &y) { x ^= y ^= x ^= y; }
def(char);
def(signed char);
def(unsigned char);
def(short);
def(unsigned short);
def(int);
def(unsigned int);
def(LL);
def(ULL);
#ifdef __SIZEOF_INT128__
def(LLL);
def(ULLL);
#endif
#undef def
}; // namespace std

#ifdef LX_LOCAL
#include <ctime>
class Time {
public:
  clock_t begin;
  Time() { begin = clock(); }
  ~Time() {
    double t = (clock() - begin) * 1000.0 / static_cast<double>(CLOCKS_PER_SEC);
    fprintf(stderr, "Time used = ");
    if (t >= 60000)
      fprintf(stderr, "%.2lfmin\n", t / 60000.0);
    else if (t >= 1000)
      fprintf(stderr, "%.2lfs\n", t / 1000.0);
    else
      fprintf(stderr, "%.0lfms\n", t);
  }
} timeout;
#endif

using std::swap;
#if __cplusplus >= 201402L
template <typename T, typename P>
inline constexpr auto max(const T &x, const P &y) {
  return x < y ? y : x;
}
template <typename T, typename P>
inline constexpr auto min(const T &x, const P &y) {
  return x < y ? x : y;
}
template <typename T, typename... Args>
inline constexpr auto max(const T &x, const Args &...args) {
  return max(x, max(args...));
}
template <typename T, typename... Args>
inline constexpr auto min(const T &x, const Args &...args) {
  return min(x, min(args...));
}
#else
template <typename T, typename P>
inline constexpr auto max(const T &x, const P &y) -> decltype(x < y ? y : x) {
  return x < y ? y : x;
}
template <typename T, typename P>
inline constexpr auto min(const T &x, const P &y) -> decltype(x < y ? x : y) {
  return x < y ? x : y;
}
template <typename T, typename... Args>
inline constexpr auto max(const T &x, const Args &...args)
    -> decltype(max(x, max(args...))) {
  return max(x, max(args...));
}
template <typename T, typename... Args>
inline constexpr auto min(const T &x, const Args &...args)
    -> decltype(min(x, min(args...))) {
  return min(x, min(args...));
}
#endif
template <typename T> inline constexpr T max(const T &x) { return x; }
template <typename T> inline constexpr T min(const T &x) { return x; }
template <typename T, typename... Args>
inline void chkmax(T &d, const Args &...args) {
  d = max(d, args...);
}
template <typename T, typename... Args>
inline void chkmin(T &d, const Args &...args) {
  d = min(d, args...);
}

#define lc (o << 1)
#define rc (o << 1 | 1)
#define lowbit(x) ((x) & (-(x)))
#define all(x) x.begin(), x.end()
#define SZ(x) int(x.size())

#pragma region IO
constexpr size_t bufSize = 1 << 20;

class In {
private:
  FILE *inFile = nullptr;
#if USE_MMAP
  struct stat st;
  char *ptr;
  int fd;
  size_t pos;
#elif !defined(LX_DEBUG)
  char buf[bufSize], *p1, *p2;
#endif
public:
#ifdef LX_DEBUG
  inline int getch() { return fgetc(inFile); }
  inline void putback(char c) { ungetc(c, inFile); }
  inline void input(FILE *f) { inFile = f; }
  inline void input(const char *str) { inFile = fopen(str, "rb"); }
#elif USE_MMAP
  inline int getch() { return *(ptr + pos) ? *(ptr + (pos++)) : EOF; }
  inline void putback(char c) { pos--; }
  inline void input(FILE *f) {
    if ((inFile = f))
      fd = fileno(inFile), fstat(fd, &st),
      ptr = (char *)mmap(0, st.st_size, PROT_READ, MAP_PRIVATE, fd, 0), pos = 0;
  }
  inline void input(const char *str) {
    fd = open(str, O_RDONLY), fstat(fd, &st),
    ptr = (char *)mmap(0, st.st_size, PROT_READ, MAP_PRIVATE, fd, 0), pos = 0;
  }
#else
  inline int getch() {
    return (p1 == p2 ? (p2 = (p1 = buf) + fread(buf, 1, bufSize, inFile)) : 0),
           (p1 == p2) ? EOF : *p1++;
  }
  inline void putback(char c) { *(--p1) = c; }
  inline void input(FILE *f) { inFile = f, p1 = p2 = buf; }
  inline void input(const char *str) {
    inFile = fopen(str, "rb"), p1 = p2 = buf;
  }
#endif
};
class Out {
private:
  FILE *outFile = nullptr;
#ifndef LX_DEBUG
  char pbuf[bufSize], *pp;
#endif
public:
#ifdef LX_DEBUG
  inline void flush() { outFile ? fflush(outFile) : 0; }
  inline void putch(const char c) { fputc(c, outFile); }
#else
  inline void flush() {
    (outFile ? fwrite(pbuf, 1, pp - pbuf, outFile), fflush(outFile) : 0),
        pp = pbuf;
  }
  inline void putch(const char c) {
    ((pp - pbuf == bufSize) ? fwrite(pbuf, 1, bufSize, outFile), pp = pbuf : 0),
        *pp++ = c;
  }
#endif
  inline void output(const char *str) { flush(), outFile = fopen(str, "wb"); }
  inline void output(FILE *f) { flush(), outFile = f; }
};
class IO : public In, public Out {
private:
  long double eps = 1e-8L;
  LLL pow10 = 1000000;
  size_t precision = 6;

public:
  IO(FILE *in = nullptr, FILE *out = nullptr);
  ~IO();
  inline void flush();
  inline static constexpr bool blank(char ch);
  template <typename T, typename... Args> bool read(T &x, Args &...args);
  template <typename T>
  typename std::enable_if<
      (std::is_signed<T>::value && std::is_integral<T>::value) ||
          std::is_same<typename std::remove_cv<T>::type, LLL>::value,
      bool>::type
  read(T &x);
  template <typename T>
  typename std::enable_if<
      (std::is_unsigned<T>::value && std::is_integral<T>::value) ||
          std::is_same<typename std::remove_cv<T>::type, ULLL>::value,
      bool>::type
  read(T &x);
  template <typename T>
  typename std::enable_if<std::is_floating_point<T>::value, bool>::type
  read(T &x);
  template <typename T>
  typename std::enable_if<
      std::is_integral<T>::value || std::is_floating_point<T>::value ||
          std::is_same<typename std::remove_cv<T>::type, LLL>::value ||
          std::is_same<typename std::remove_cv<T>, ULLL>::value,
      T>::type
  read();
  bool read(char &ch);
  bool read(char *s);
  bool readline(char *s);
  inline void setprecision(size_t n = 6u);
  template <typename T, typename... Args>
  void write(const T &x, const Args &...args);
  inline void write() const {}
  template <typename T>
  typename std::enable_if<(std::is_signed<T>::value &&
                           std::is_integral<T>::value) ||
                              std::is_same<T, LLL>::value,
                          void>::type
  write(T x);
  template <typename T>
  typename std::enable_if<(std::is_unsigned<T>::value &&
                           std::is_integral<T>::value) ||
                              std::is_same<T, ULLL>::value,
                          void>::type
  write(T x);
  inline void write(char c);
  template <typename T>
  typename std::enable_if<std::is_floating_point<T>::value, void>::type
  write(T x);
  inline void write(bool x);
  void write(char *s);
  void write(const char *s);
  template <typename... Args> void writeln(Args... x);
} io(stdin, stdout), err(nullptr, stderr);
template <typename... Args> inline void writeln(Args... x) {
  io.write(x...), io.putch('\n');
}
#define dbg(x) err.write(#x " = "), err.writeln(x)
#pragma endregion IO
#include <map>
const int maxn = 200005;

int A[maxn];
int main() {
  int n;
  io.read(n);
  for (int i = 1; i <= n; i++)
    io.read(A[i]);
  std::map<int, int> mp, mp2;
  for (int i = 1; i <= n; i++)
    mp[i - A[i]]++;
  LL ans = 0;
  for (int i = 1; i <= n; i++)
    ans += mp[A[i] + i];
  writeln(ans);
  return 0;
}

#define isdigit(x) (x >= '0' && x <= '9')
IO::IO(FILE *in, FILE *out) { input(in), output(out); }
IO::~IO() { flush(); }
inline void IO::flush() { Out::flush(); }
inline constexpr bool IO::blank(char ch) {
  return ch == ' ' || ch == '\n' || ch == '\r' || ch == '\t';
}
template <typename T, typename... Args> bool IO::read(T &x, Args &...args) {
  return read(x) && (sizeof...(args) ? read(args...) : true);
}
template <typename T>
typename std::enable_if<
    (std::is_signed<T>::value && std::is_integral<T>::value) ||
        std::is_same<typename std::remove_cv<T>::type, LLL>::value,
    bool>::type
IO::read(T &x) {
  x = 0;
  bool sign = false;
  int ch = getch();
  while (!isdigit(ch) && ~ch)
    sign &= (ch == '-'), ch = getch();
  if (!(~ch))
    return false;
  while (isdigit(ch))
    x = (x << 1) + (x << 3) + (ch ^ '0'), ch = getch();
  if (~ch)
    putback(ch);
  x = sign ? (~x + 1) : x;
  return true;
}
template <typename T>
typename std::enable_if<
    (std::is_unsigned<T>::value && std::is_integral<T>::value) ||
        std::is_same<typename std::remove_cv<T>::type, ULLL>::value,
    bool>::type
IO::read(T &x) {
  x = 0;
  int ch = getch();
  while (!isdigit(ch) && ~ch)
    ch = getch();
  if (!(~ch))
    return false;
  while (isdigit(ch))
    x = (x << 1) + (x << 3) + (ch ^ '0'), ch = getch();
  if (~ch)
    putback(ch);
  return true;
}
template <typename T>
typename std::enable_if<std::is_floating_point<T>::value, bool>::type
IO::read(T &x) {
  x = 0;
  T tmp = 1;
  bool sign = false;
  int ch = getch();
  while (!isdigit(ch) && ~ch)
    sign &= (ch == '-'), ch = getch();
  if (!(~ch))
    return false;
  while (isdigit(ch))
    x = x * 10 + (ch ^ '0'), ch = getch();
  if (ch == '.')
    for (ch = getch(); isdigit(ch); ch = getch())
      x += (tmp /= 10.0) * (ch ^ '0');
  if (~ch)
    putback(ch);
  x = sign ? (-x) : x;
  return true;
}
template <typename T>
typename std::enable_if<
    std::is_integral<T>::value || std::is_floating_point<T>::value ||
        std::is_same<typename std::remove_cv<T>::type, LLL>::value ||
        std::is_same<typename std::remove_cv<T>, ULLL>::value,
    T>::type
IO::read() {
  typename std::remove_cv<T>::type x;
  read(x);
  return x;
}
bool IO::read(char &ch) {
  do
    ch = getch();
  while (blank(ch) && ~ch);
  return ~ch;
}
bool IO::read(char *s) {
  int ch = getch();
  while (blank(ch))
    ch = getch();
  if (!(~ch))
    return false;
  while (!blank(ch) && ~ch)
    *s++ = ch, ch = getch();
  *s = 0;
  if (~ch)
    putback(ch);
  return true;
}
bool IO::readline(char *s) {
  int ch = getch();
  while (blank(ch) && (ch ^ '\n'))
    ch = getch();
  if (!(~ch))
    return false;
  while ((ch ^ '\n') && ~ch)
    *s++ = ch, ch = getch();
  *s = 0;
  if (~ch)
    putback(ch);
  return true;
}
inline void IO::setprecision(size_t n) {
  precision = n;
  eps = powl(10.0L, -precision - 2);
  pow10 = powl(10.0L, precision) + eps;
}
template <typename T, typename... Args>
void IO::write(const T &x, const Args &...args) {
  write(x);
  if (sizeof...(args))
    write(args...);
}
template <typename T>
typename std::enable_if<(std::is_signed<T>::value &&
                         std::is_integral<T>::value) ||
                            std::is_same<T, LLL>::value,
                        void>::type
IO::write(T x) {
  if (x < 0)
    x = ~x + 1, putch('-');
  static int sta[40], top = 0;
  do
    sta[top++] = x % 10, x /= 10;
  while (x);
  while (top)
    putch(sta[--top] ^ '0');
}
template <typename T>
typename std::enable_if<(std::is_unsigned<T>::value &&
                         std::is_integral<T>::value) ||
                            std::is_same<T, ULLL>::value,
                        void>::type
IO::write(T x) {
  static int sta[40], top = 0;
  do
    sta[top++] = x % 10, x /= 10;
  while (x);
  while (top)
    putch(sta[--top] ^ '0');
}
inline void IO::write(bool x) { putch(x ^ 48); }
inline void IO::write(char c) { putch(c); }
template <typename T>
typename std::enable_if<std::is_floating_point<T>::value>::type IO::write(T x) {
  if (x == 0) {
    putch('0'), putch('.');
    for (int i = 1; i <= precision; i++)
      putch('0');
    return;
  }
  if (x < 0)
    putch('-'), x = -x;
  T res = (LLL)(x * pow10 + 0.5) / (pow10 * 1.0);
  LLL y = LLL(res * pow10 + eps) % pow10;
  write(LLL(res + eps));
  if (precision) {
    putch('.');
    static int sta[100], p = 0;
    while (p < precision)
      sta[++p] = y % 10, y /= 10;
    for (int i = p; i >= 1; i--)
      putch(sta[i] ^ 48);
  }
}
void IO::write(char *s) {
  while (*s)
    putch(*s++);
}
void IO::write(const char *s) {
  while (*s)
    putch(*s++);
}
template <typename... Args> void IO::writeln(Args... x) {
  write(x...), putch('\n');
}
#undef isdigit