Problem p02755 (C++)

Buggy submission (status: Time Limit Exceeded):
#include <bits/stdc++.h>
#define rep(i, n) for (int i = 0; i < (int)n; ++i)
#define REP(i, a, b) for (int i = int(a); i < (int)b; ++i)
#define Graph vector<vecctor<ll>>
#define pairs vector<pair<ll, ll>>
#define pb push_back

using namespace std;
using ll = long long;
const ll INF = 1e18;
const double PI = acos(-1);

template <class T> inline bool chmin(T &a, T b) {
  if (a > b) {
    a = b;
    return true;
  }
  return false;
}
template <class T> inline bool chmax(T &a, T b) {
  if (a < b) {
    a = b;
    return true;
  }
  return false;
}
const ll mod = 1000000007;
struct mint {
  ll x; // typedef long long ll;
  mint(ll x = 0) : x((x % mod + mod) % mod) {}
  mint operator-() const { return mint(-x); }
  mint &operator+=(const mint a) {
    if ((x += a.x) >= mod)
      x -= mod;
    return *this;
  }
  mint &operator-=(const mint a) {
    if ((x += mod - a.x) >= mod)
      x -= mod;
    return *this;
  }
  mint &operator*=(const mint a) {
    (x *= a.x) %= mod;
    return *this;
  }
  mint operator+(const mint a) const { return mint(*this) += a; }
  mint operator-(const mint a) const { return mint(*this) -= a; }
  mint operator*(const mint a) const { return mint(*this) *= a; }
  mint pow(ll t) const {
    if (!t)
      return 1;
    mint a = pow(t >> 1);
    a *= a;
    if (t & 1)
      a *= *this;
    return a;
  }

  // for prime mod
  mint inv() const { return pow(mod - 2); }
  mint &operator/=(const mint a) { return *this *= a.inv(); }
  mint operator/(const mint a) const { return mint(*this) /= a; }
};
istream &operator>>(istream &is, const mint &a) { return is >> a.x; }
ostream &operator<<(ostream &os, const mint &a) { return os << a.x; }

struct combination {
  vector<mint> fact, ifact;
  combination(int n) : fact(n + 1), ifact(n + 1) {
    assert(n < mod);
    fact[0] = 1;
    for (int i = 1; i <= n; ++i) {
      fact[i] = fact[i - 1] * i;
    }
    ifact[n] = fact[n].inv();
    for (int i = n; i >= 1; --i) {
      ifact[i - 1] = ifact[i] * i;
    }
  }
  mint operator()(int n, int k) {
    if (k < 0 || k > n)
      return 0;
    return fact[n] * ifact[k] * ifact[n - k];
  }
};

ll modpow(ll p, ll q) {
  if (q == 0)
    return 1;
  if (q % 2 == 0) {
    ll x = modpow(p, q / 2);
    return x * x % mod;
  } else {
    return modpow(p, q - 1) * p % mod;
  }
}

ll choose(ll n, ll k) {
  ll x = 1, y = 1;
  rep(i, k) {
    x = x * (n - i) % mod;
    y = y * (k - i) % mod;
  }
  y = modpow(y, mod - 2);
  return x * y % mod;
}

int main(void) {
  std::cin.tie(nullptr);
  std::ios::sync_with_stdio(false);
  int a, b, ans = 1e8;
  cin >> a >> b;
  for (int i = 20000; i > 0; ++i) {
    int p = i * 8 / 100, q = i * 10 / 100;
    if (p == a && q == b) {
      ans = i;
    }
  }
  if (ans == 1e8)
    cout << -1 << endl;
  else
    cout << ans << endl;
  return 0;
}


Fixed submission:
#include <bits/stdc++.h>
#define rep(i, n) for (int i = 0; i < (int)n; ++i)
#define REP(i, a, b) for (int i = int(a); i < (int)b; ++i)
#define Graph vector<vecctor<ll>>
#define pairs vector<pair<ll, ll>>
#define pb push_back

using namespace std;
using ll = long long;
const ll INF = 1e18;
const double PI = acos(-1);

template <class T> inline bool chmin(T &a, T b) {
  if (a > b) {
    a = b;
    return true;
  }
  return false;
}
template <class T> inline bool chmax(T &a, T b) {
  if (a < b) {
    a = b;
    return true;
  }
  return false;
}
const ll mod = 1000000007;
struct mint {
  ll x; // typedef long long ll;
  mint(ll x = 0) : x((x % mod + mod) % mod) {}
  mint operator-() const { return mint(-x); }
  mint &operator+=(const mint a) {
    if ((x += a.x) >= mod)
      x -= mod;
    return *this;
  }
  mint &operator-=(const mint a) {
    if ((x += mod - a.x) >= mod)
      x -= mod;
    return *this;
  }
  mint &operator*=(const mint a) {
    (x *= a.x) %= mod;
    return *this;
  }
  mint operator+(const mint a) const { return mint(*this) += a; }
  mint operator-(const mint a) const { return mint(*this) -= a; }
  mint operator*(const mint a) const { return mint(*this) *= a; }
  mint pow(ll t) const {
    if (!t)
      return 1;
    mint a = pow(t >> 1);
    a *= a;
    if (t & 1)
      a *= *this;
    return a;
  }

  // for prime mod
  mint inv() const { return pow(mod - 2); }
  mint &operator/=(const mint a) { return *this *= a.inv(); }
  mint operator/(const mint a) const { return mint(*this) /= a; }
};
istream &operator>>(istream &is, const mint &a) { return is >> a.x; }
ostream &operator<<(ostream &os, const mint &a) { return os << a.x; }

struct combination {
  vector<mint> fact, ifact;
  combination(int n) : fact(n + 1), ifact(n + 1) {
    assert(n < mod);
    fact[0] = 1;
    for (int i = 1; i <= n; ++i) {
      fact[i] = fact[i - 1] * i;
    }
    ifact[n] = fact[n].inv();
    for (int i = n; i >= 1; --i) {
      ifact[i - 1] = ifact[i] * i;
    }
  }
  mint operator()(int n, int k) {
    if (k < 0 || k > n)
      return 0;
    return fact[n] * ifact[k] * ifact[n - k];
  }
};

ll modpow(ll p, ll q) {
  if (q == 0)
    return 1;
  if (q % 2 == 0) {
    ll x = modpow(p, q / 2);
    return x * x % mod;
  } else {
    return modpow(p, q - 1) * p % mod;
  }
}

ll choose(ll n, ll k) {
  ll x = 1, y = 1;
  rep(i, k) {
    x = x * (n - i) % mod;
    y = y * (k - i) % mod;
  }
  y = modpow(y, mod - 2);
  return x * y % mod;
}

int main(void) {
  std::cin.tie(nullptr);
  std::ios::sync_with_stdio(false);
  int a, b, ans = 1e8;
  cin >> a >> b;
  for (int i = 20000; i > 0; --i) {
    int p = i * 8 / 100, q = i * 10 / 100;
    if (p == a && q == b) {
      ans = i;
    }
  }
  if (ans == 1e8)
    cout << -1 << endl;
  else
    cout << ans << endl;
  return 0;
}