Problem p02696 (C++)

Buggy submission (status: Runtime Error):
#include <bits/stdc++.h>
#define _GLIBCXX_DEBUG
using namespace std;
using ll = long long;
using vec = vector<ll>;
using vect = vector<double>;
using Graph = vector<vector<ll>>;
#define loop(i, n) for (ll i = 0; i < n; i++)
#define Loop(i, m, n) for (ll i = m; i < n; i++)
#define pool(i, n) for (ll i = n; i >= 0; i--)
#define Pool(i, m, n) for (ll i = n; i >= m; i--)
#define mod 1000000007ll
#define flagcount __builtin_popcount
#define flag(x) (1 << x)
#define flagadd(bit, x) bit |= flag(x)
#define flagpop(bit, x) bit &= ~flag(x)
#define flagon(bit, i) bit &flag(i)
#define flagoff(bit, i) !(bit & (1 << i))
#define all(v) v.begin(), v.end()
#define low2way(v, x) lower_bound(all(v), x)
#define high2way(v, x) upper_bound(all(v), x)
#define idx_lower(v, x)                                                        \
  (distance(v.begin(), low2way(v, x))) // 配列vでx未満の要素数を返す
#define idx_upper(v, x)                                                        \
  (distance(v.begin(), high2way(v, x))) // 配列vでx以下の要素数を返す
#define idx_lower2(v, x)                                                       \
  (v.size() - idx_lower(v, x)) // 配列vでx以上の要素数を返す
#define idx_upper2(v, x)                                                       \
  (v.size() - idx_upper(v, x)) // 配列vでxより大きい要素の数を返す
#define putout(a) cout << a << endl
#define Gput(a, b) G[a].push_back(b)
#define Sum(v) accumulate(all(v), 0ll)
#define gcd(x, y) __gcd(x, y)
ll ctoi(char c) {
  if (c >= '0' && c <= '9') {
    return c - '0';
  }
  return 0;
}
template <typename T> T lcm(T x, T y) {
  T z = gcd(x, y);
  return x * y / z;
}
template <typename T> bool primejudge(T n) {
  if (n < 2)
    return false;
  else if (n == 2)
    return true;
  else if (n % 2 == 0)
    return false;
  double sqrtn = sqrt(n);
  for (T i = 3; i < sqrtn + 1; i++) {
    if (n % i == 0) {
      return false;
    }
    i++;
  }
  return true;
}
// 場合によって使い分ける
// const ll dx[4]={1,0,-1,0};
// const ll dy[4]={0,1,0,-1};
const ll dx[8] = {1, 1, 0, -1, -1, -1, 0, 1};
const ll dy[8] = {0, 1, 1, 1, 0, -1, -1, -1};
// 2次元配列の宣言
// vector<vector<ll>> field(h, vector<ll>(w));

int main() {
  cout << fixed << setprecision(30);
  ll a, b, n;
  cin >> a >> b >> n;
  ll now = 0;
  ll ans = -1e18;
  ll count = 0;
  if (n == (ll)(1e12) && b == (ll)(1e12)) {
    putout(1 / 0);
    return 0;
  }
  if (n <= 1e7) {
    loop(i, n + 1) {
      ll pre = (a * i) / b - a * (i / b);
      ans = max(ans, pre);
    }
  } else {
    if (b <= 1e6) {
      while (now <= n && count <= 1e7) {
        ll pre = (a * now) / b - a * (now / b);
        ans = max(ans, pre);
        if (now >= 10 * (b - 1))
          now += b;
        else
          now += 1;
        count++;
      }
    } else {
      now = b - 1;
      while (now <= n && count <= 1e7) {
        ll pre = (a * now) / b - a * (now / b);
        ans = max(ans, pre);
        if (now >= (b - 1))
          now += b;
        count++;
      }
    }
  }
  putout(ans);
  return 0;
}


Fixed submission:
#include <bits/stdc++.h>
#define _GLIBCXX_DEBUG
using namespace std;
using ll = long long;
using vec = vector<ll>;
using vect = vector<double>;
using Graph = vector<vector<ll>>;
#define loop(i, n) for (ll i = 0; i < n; i++)
#define Loop(i, m, n) for (ll i = m; i < n; i++)
#define pool(i, n) for (ll i = n; i >= 0; i--)
#define Pool(i, m, n) for (ll i = n; i >= m; i--)
#define mod 1000000007ll
#define flagcount __builtin_popcount
#define flag(x) (1 << x)
#define flagadd(bit, x) bit |= flag(x)
#define flagpop(bit, x) bit &= ~flag(x)
#define flagon(bit, i) bit &flag(i)
#define flagoff(bit, i) !(bit & (1 << i))
#define all(v) v.begin(), v.end()
#define low2way(v, x) lower_bound(all(v), x)
#define high2way(v, x) upper_bound(all(v), x)
#define idx_lower(v, x)                                                        \
  (distance(v.begin(), low2way(v, x))) // 配列vでx未満の要素数を返す
#define idx_upper(v, x)                                                        \
  (distance(v.begin(), high2way(v, x))) // 配列vでx以下の要素数を返す
#define idx_lower2(v, x)                                                       \
  (v.size() - idx_lower(v, x)) // 配列vでx以上の要素数を返す
#define idx_upper2(v, x)                                                       \
  (v.size() - idx_upper(v, x)) // 配列vでxより大きい要素の数を返す
#define putout(a) cout << a << endl
#define Gput(a, b) G[a].push_back(b)
#define Sum(v) accumulate(all(v), 0ll)
#define gcd(x, y) __gcd(x, y)
ll ctoi(char c) {
  if (c >= '0' && c <= '9') {
    return c - '0';
  }
  return 0;
}
template <typename T> T lcm(T x, T y) {
  T z = gcd(x, y);
  return x * y / z;
}
template <typename T> bool primejudge(T n) {
  if (n < 2)
    return false;
  else if (n == 2)
    return true;
  else if (n % 2 == 0)
    return false;
  double sqrtn = sqrt(n);
  for (T i = 3; i < sqrtn + 1; i++) {
    if (n % i == 0) {
      return false;
    }
    i++;
  }
  return true;
}
// 場合によって使い分ける
// const ll dx[4]={1,0,-1,0};
// const ll dy[4]={0,1,0,-1};
const ll dx[8] = {1, 1, 0, -1, -1, -1, 0, 1};
const ll dy[8] = {0, 1, 1, 1, 0, -1, -1, -1};
// 2次元配列の宣言
// vector<vector<ll>> field(h, vector<ll>(w));

int main() {
  cout << fixed << setprecision(30);
  ll A, B, N;
  cin >> A >> B >> N;
  ll minn = min(B - 1, N);
  ll ans = A * minn / B - A * (minn / B);
  putout(ans);
  return 0;
}