Problem p02724 (C++)

Buggy submission (status: Runtime Error):
/*Author SHUBH AGRAWAL  */

#include <bits/stdc++.h>
using namespace std;
#define pb push_back
#define pu push //  adds the value to the last of the queue
#define lld long long int
#define ins insert  /// used in set to insert the values
#define adv advance /// used to increment the iterator
#define mp make_pair
#define fi first
#define se second
#define all(c) c.begin(), c.end()
#define PI 3.1415926
// a power n mod p

#define vl vector<long long int>
#define vpl vector<pair<lld, lld>>
#define vvl vector<vector<lld>>

long long int modp(lld a, lld p, lld n) {
  int d[100];
  int i, j, k, l;
  if (n == 0)
    return 1;
  for (i = 0; n >= 1; i++) {
    d[i] = n % 2;
    n /= 2;
  }
  l = i;
  long long int e = 1;
  if (d[0] == 1)
    e *= (a % p);
  for (i = 1; i < l; i++) {
    a *= a;
    a = a % p;
    if (d[i] == 1) {
      e *= a;
      e = e % p;
    }
  }
  return e % p;
}
lld modInverse(lld n, lld p) { return modp(n, p, p - 2); }

long long int nCrModPFermat(lld n, lld r, lld p) {
  // Base case
  if (r == 0)
    return 1;

  // Fill factorial array so that we
  // can find all factorial of r, n
  // and n-r
  lld fac[n + 1];
  fac[0] = 1;
  for (lld i = 1; i <= n; i++)
    fac[i] = fac[i - 1] * i % p;

  return (fac[n] * modInverse(fac[r], p) % p * modInverse(fac[n - r], p) % p) %
         p;
}

long long int gcd(lld b, lld a) {
  if (a < b)
    return gcd(a, b);
  if (a % b == 0)
    return b;
  return gcd(a % b, b);
}

lld l, r, mid, ans;
lld n, m, i, j, k, x;

char c;
void solve() {
  cin >> n;
  ans = (n / 500) * 1000;
  n -= (n / 500) * 500;
  ans += (n / 5) * 5;
  cout << ans;
  //   cout<<"\n";
}

int main() {
#ifndef ONLINE_JUDGE
  // for getting input from input.txt
  freopen("input.txt", "r", stdin);
  // for writing output to output.txt
  freopen("output.txt", "w", stdout);
#endif
  ios_base::sync_with_stdio(false);
  cin.tie(NULL);
  lld t = 1;
  // cin>>t;
  while (t--) {
    solve();
  }
  return 0;
}

Fixed submission:
/*Author SHUBH AGRAWAL  */

#include <bits/stdc++.h>
using namespace std;
#define pb push_back
#define pu push //  adds the value to the last of the queue
#define lld long long int
#define ins insert  /// used in set to insert the values
#define adv advance /// used to increment the iterator
#define mp make_pair
#define fi first
#define se second
#define all(c) c.begin(), c.end()
#define PI 3.1415926
// a power n mod p

#define vl vector<long long int>
#define vpl vector<pair<lld, lld>>
#define vvl vector<vector<lld>>

long long int modp(lld a, lld p, lld n) {
  int d[100];
  int i, j, k, l;
  if (n == 0)
    return 1;
  for (i = 0; n >= 1; i++) {
    d[i] = n % 2;
    n /= 2;
  }
  l = i;
  long long int e = 1;
  if (d[0] == 1)
    e *= (a % p);
  for (i = 1; i < l; i++) {
    a *= a;
    a = a % p;
    if (d[i] == 1) {
      e *= a;
      e = e % p;
    }
  }
  return e % p;
}
lld modInverse(lld n, lld p) { return modp(n, p, p - 2); }

long long int nCrModPFermat(lld n, lld r, lld p) {
  // Base case
  if (r == 0)
    return 1;

  // Fill factorial array so that we
  // can find all factorial of r, n
  // and n-r
  lld fac[n + 1];
  fac[0] = 1;
  for (lld i = 1; i <= n; i++)
    fac[i] = fac[i - 1] * i % p;

  return (fac[n] * modInverse(fac[r], p) % p * modInverse(fac[n - r], p) % p) %
         p;
}

long long int gcd(lld b, lld a) {
  if (a < b)
    return gcd(a, b);
  if (a % b == 0)
    return b;
  return gcd(a % b, b);
}

lld l, r, mid, ans;
lld n, m, i, j, k, x;

char c;
void solve() {
  cin >> n;
  ans = (n / 500) * 1000;
  n -= (n / 500) * 500;
  ans += (n / 5) * 5;
  cout << ans;
  //   cout<<"\n";
}

int main() {
  ios_base::sync_with_stdio(false);
  cin.tie(NULL);
  lld t = 1;
  // cin>>t;
  while (t--) {
    solve();
  }
  return 0;
}