Problem p02623 (C++) — buggy submission, verdict: Runtime Error

#include <bits/stdc++.h>
using namespace std;
#define rep(i, n) for (ll i = 0; i < n; i++)
#define repl(i, l, r) for (ll i = (l); i < (r); i++)
#define per(i, n) for (ll i = n - 1; i >= 0; i--)
#define perl(i, r, l) for (ll i = r - 1; i >= l; i--)
#define fi first
#define se second
#define pb push_back
#define ins insert
#define pqueue(x) priority_queue<x, vector<x>, greater<x>>
#define all(x) (x).begin(), (x).end()
#define CST(x) cout << fixed << setprecision(x)
#define vtpl(x, y, z) vector<tuple<x, y, z>>
#define rev(x) reverse(x);
using ll = long long;
using vl = vector<ll>;
using vvl = vector<vector<ll>>;
using pl = pair<ll, ll>;
using vpl = vector<pl>;
using vvpl = vector<vpl>;
const ll MOD = 1000000007;
const ll MOD9 = 998244353;
const int inf = 1e9 + 10;
const ll INF = 4e18;
const ll dy[8] = {1, 0, -1, 0, 1, 1, -1, -1};
const ll dx[8] = {0, -1, 0, 1, 1, -1, 1, -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;
}
int main() {
  ll n, m;
  cin >> n >> m;
  ll k;
  cin >> k;
  vl a(n), b(m);
  rep(i, n) cin >> a[i];
  rep(i, m) cin >> b[i];
  rep(i, m - 1) b[i + 1] += b[i];
  rep(i, n - 1) a[i + 1] += a[i];
  // rep(i,m)cout << b[i] <<" ";
  ll res = 0;
  ll p = upper_bound(all(b), k) - b.begin();
  res = p;
  rep(i, n) {
    ll t = k - a[i];
    if (t < 0)
      continue;
    ll p = upper_bound(all(b), t) - b.begin();
    // cout << p <<endl;
    chmax(res, p + i + 1);
  }
  cout << res << endl;
}

Error: 0

Fixed submission:

#include <bits/stdc++.h>
using namespace std;
#define rep(i, n) for (ll i = 0; i < n; i++)
#define repl(i, l, r) for (ll i = (l); i < (r); i++)
#define per(i, n) for (ll i = n - 1; i >= 0; i--)
#define perl(i, r, l) for (ll i = r - 1; i >= l; i--)
#define fi first
#define se second
#define pb push_back
#define ins insert
#define pqueue(x) priority_queue<x, vector<x>, greater<x>>
#define all(x) (x).begin(), (x).end()
#define CST(x) cout << fixed << setprecision(x)
#define vtpl(x, y, z) vector<tuple<x, y, z>>
#define rev(x) reverse(x);
using ll = long long;
using vl = vector<ll>;
using vvl = vector<vector<ll>>;
using pl = pair<ll, ll>;
using vpl = vector<pl>;
using vvpl = vector<vpl>;
const ll MOD = 1000000007;
const ll MOD9 = 998244353;
const int inf = 1e9 + 10;
const ll INF = 4e18;
const ll dy[8] = {1, 0, -1, 0, 1, 1, -1, -1};
const ll dx[8] = {0, -1, 0, 1, 1, -1, 1, -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;
}
int main() {
  ll n, m;
  cin >> n >> m;
  ll k;
  cin >> k;
  vl a(n), b(m);
  rep(i, n) cin >> a[i];
  rep(i, m) cin >> b[i];
  rep(i, m - 1) b[i + 1] += b[i];
  rep(i, n - 1) a[i + 1] += a[i];
  /*rep(i,n)cout << a[i] <<" ";
 cout << endl;
 rep(i,m)cout << b[i] <<" ";
 cout << endl;*/
  ll res = 0;
  ll now = -1;
  per(i, n) {
    ll t = k - a[i];
    if (t < 0)
      continue;
    while (now < n && b[now + 1] <= t) {
      now++;
    }
    // cout << now <<endl;
    chmax(res, now + i + 2);
  }
  cout << res << endl;
}