Problem p02696 (C++)

Buggy submission (status: Time Limit Exceeded):
#include <bits/stdc++.h>
using namespace std;
typedef long long ll;
#define FOR(var, begin, end) for (int var = (begin); var <= (end); var++)
#define RFOR(var, begin, end) for (int var = (begin); var >= (end); var--)
#define REP(var, length) FOR(var, 0, length - 1)
#define RREP(var, length) RFOR(var, length - 1, 0)
#define EACH(value, var) for (auto value : var)
#define SORT(var) sort(var.begin(), var.end())
#define REVERSE(var) reverse(var.begin(), var.end())
#define RSORT(var)                                                             \
  SORT(var);                                                                   \
  REVERSE(var)
#define OPTIMIZE_STDIO                                                         \
  ios::sync_with_stdio(false);                                                 \
  cin.tie(0);                                                                  \
  cout.precision(10);                                                          \
  cout << fixed
#define endl '\n'

const int INF = 1e9;
const ll MOD = 1e9 + 7;
const ll LINF = 1e18;
struct mint {
  ll x;
  mint() : x(0) {}
  mint(ll x) : x((x % MOD + MOD) % MOD) {}
  mint &operator+=(const mint &r) {
    if ((x += r.x) >= MOD) {
      x -= MOD;
    }
    return *this;
  }
  mint &operator-=(const mint &r) {
    if ((x -= r.x) < 0) {
      x += MOD;
    }
    return *this;
  }
  mint &operator*=(const mint &r) {
    if ((x *= r.x) > MOD) {
      x %= MOD;
    }
    return *this;
  }
  mint &operator++() {
    if ((++x) >= MOD) {
      x -= MOD;
    }
    return *this;
  }
  mint operator++(int) {
    mint ret = x;
    if ((++x) >= MOD) {
      x -= MOD;
    }
    return ret;
  }
  mint &operator--() {
    if ((--x) < 0) {
      x += MOD;
    }
    return *this;
  }
  mint operator--(int) {
    mint ret = x;
    if ((--x) < 0) {
      x += MOD;
    }
    return ret;
  }
  mint operator+(const mint &r) {
    mint ret;
    return ret = x + r.x;
  }
  mint operator-(const mint &r) {
    mint ret;
    return ret = x - r.x;
  }
  mint operator*(const mint &r) {
    mint ret;
    return ret = x * r.x;
  }
  mint operator-() { return mint() - *this; }
  bool operator<(const mint &a) { return x < a.x; }
  bool operator>(const mint &a) { return x > a.x; }
  bool operator<=(const mint &a) { return x <= a.x; }
  bool operator>=(const mint &a) { return x >= a.x; }
  bool operator==(const mint &a) { return x == a.x; }
  bool operator!=(const mint &a) { return x != a.x; }
};
ostream &operator<<(ostream &os, const mint &r) {
  os << r.x;
  return os;
}
ostream &operator>>(ostream &os, const mint &r) {
  os >> r.x;
  return os;
}

ll a, b, n;
ll ans;

void solve(istream &cin, ostream &cout) {
  cin >> a >> b >> n;
  ll r = min(b - 1, n);
  ll ans = -LINF;
  for (ll i = 0; i <= r; i++) {
    ll tmp = floor(a * i / b) - a * floor(i / b);
    ans = max(ans, tmp);
  }
  cout << ans << endl;
}

#ifndef TEST
int main() {
  OPTIMIZE_STDIO;
  solve(cin, cout);
  return 0;
}
#endif


Fixed submission:
#include <bits/stdc++.h>
using namespace std;
typedef long long ll;
#define FOR(var, begin, end) for (int var = (begin); var <= (end); var++)
#define RFOR(var, begin, end) for (int var = (begin); var >= (end); var--)
#define REP(var, length) FOR(var, 0, length - 1)
#define RREP(var, length) RFOR(var, length - 1, 0)
#define EACH(value, var) for (auto value : var)
#define SORT(var) sort(var.begin(), var.end())
#define REVERSE(var) reverse(var.begin(), var.end())
#define RSORT(var)                                                             \
  SORT(var);                                                                   \
  REVERSE(var)
#define OPTIMIZE_STDIO                                                         \
  ios::sync_with_stdio(false);                                                 \
  cin.tie(0);                                                                  \
  cout.precision(10);                                                          \
  cout << fixed
#define endl '\n'

const int INF = 1e9;
const ll MOD = 1e9 + 7;
const ll LINF = 1e18;
struct mint {
  ll x;
  mint() : x(0) {}
  mint(ll x) : x((x % MOD + MOD) % MOD) {}
  mint &operator+=(const mint &r) {
    if ((x += r.x) >= MOD) {
      x -= MOD;
    }
    return *this;
  }
  mint &operator-=(const mint &r) {
    if ((x -= r.x) < 0) {
      x += MOD;
    }
    return *this;
  }
  mint &operator*=(const mint &r) {
    if ((x *= r.x) > MOD) {
      x %= MOD;
    }
    return *this;
  }
  mint &operator++() {
    if ((++x) >= MOD) {
      x -= MOD;
    }
    return *this;
  }
  mint operator++(int) {
    mint ret = x;
    if ((++x) >= MOD) {
      x -= MOD;
    }
    return ret;
  }
  mint &operator--() {
    if ((--x) < 0) {
      x += MOD;
    }
    return *this;
  }
  mint operator--(int) {
    mint ret = x;
    if ((--x) < 0) {
      x += MOD;
    }
    return ret;
  }
  mint operator+(const mint &r) {
    mint ret;
    return ret = x + r.x;
  }
  mint operator-(const mint &r) {
    mint ret;
    return ret = x - r.x;
  }
  mint operator*(const mint &r) {
    mint ret;
    return ret = x * r.x;
  }
  mint operator-() { return mint() - *this; }
  bool operator<(const mint &a) { return x < a.x; }
  bool operator>(const mint &a) { return x > a.x; }
  bool operator<=(const mint &a) { return x <= a.x; }
  bool operator>=(const mint &a) { return x >= a.x; }
  bool operator==(const mint &a) { return x == a.x; }
  bool operator!=(const mint &a) { return x != a.x; }
};
ostream &operator<<(ostream &os, const mint &r) {
  os << r.x;
  return os;
}
ostream &operator>>(ostream &os, const mint &r) {
  os >> r.x;
  return os;
}

ll a, b, n;
ll ans;

void solve(istream &cin, ostream &cout) {
  cin >> a >> b >> n;
  ll r = min(b - 1, n);
  ll ans = floor(a * r / b) - a * floor(r / b);
  cout << ans << endl;
}

#ifndef TEST
int main() {
  OPTIMIZE_STDIO;
  solve(cin, cout);
  return 0;
}
#endif