Problem p02623 (C++)

Buggy submission (status: Runtime Error):
#include <bits/stdc++.h>
#include <ext/pb_ds/assoc_container.hpp>
#include <ext/pb_ds/tree_policy.hpp>

using namespace __gnu_pbds;
using namespace std;

#pragma GCC optimize("Ofast")
#pragma GCC target("avx,avx2,fma")
#pragma GCC optimization("unroll-loops")

#define fast                                                                   \
  ios_base::sync_with_stdio(false);                                            \
  cin.tie(NULL);                                                               \
  cout.tie(NULL);
#define ll long long int
#define ull unsigned long long
#define ld long double

#define mod 1000000007
#define EULER 2.7182818284
#define INF 1000000000

#define pb push_back
#define ins insert
#define IT iterator
#define PQ priority_queue
#define nl "\n"
#define fi first
#define se second
#define maxe max_element
#define mine min_element
#define er erase
#define lb lower_bound
#define ub upper_bound

#define vi vector<int>
#define vll vector<ll>
#define vb vector<bool>
#define pi pair<int, int>
#define pll pair<ll, ll>
#define all(v) v.begin(), v.end()

#define mem(v, i)                                                              \
  memset(                                                                      \
      v, i,                                                                    \
      sizeof(                                                                  \
          v)) // v is array. To set all elements to 0 or -1 only. mem(arr,0);

#define repab(i, a, b) for (int i = (a); i <= (b); i++)
#define reprab(i, a, b) for (int i = (a); i >= (b); i--)
#define repll(i, a, b) for (ll i = (a); i <= (b); i++)
#define rep(i, n) for (int i = (0); i < (n); i++)
#define repr(i, n) for (int i = (n); i >= 0; i--)
#define bs bitset
#define bpc(a) __builtin_popcount(a)
#define tc                                                                     \
  int t;                                                                       \
  cin >> t;                                                                    \
  while (t--)
template <typename T> void TIME(T start, T end) {
#ifndef ONLINE_JUDGE
  double time_taken =
      chrono::duration_cast<chrono::nanoseconds>(end - start).count();
  time_taken *= 1e-9;
  cout << "\nExecuted in: " << fixed << time_taken << setprecision(9);
  cout << " sec";
#endif
}

int dx[] = {1, -1, 0, 0};
int dy[] = {0, 0, 1, -1};

ll max(ll a, ll b) {
  if (a > b)
    return a;
  return b;
}
ll min(ll a, ll b) {
  if (a < b)
    return a;
  return b;
}

ll mypow(ll a, ll b) {
  ll res = 1;
  while (b > 0) {
    if (b & 1)
      res = res * a;
    a = a * a;
    b >>= 1;
  }
  return res;
}
ll gcd(ll a, ll b) {
  if (b == 0)
    return a;
  return gcd(b, a % b);
}
//..............................!!!!!!Get ready to
//fight!!!!!!............................

int main() {
  auto start = chrono::high_resolution_clock::now();
  fast ll n, m, k;
  cin >> n >> m >> k;
  vll a(n + 1), b(m + 1);
  rep(i, n) cin >> a[i];
  rep(i, m) cin >> b[i];
  vll suma(n + 1), sumb(n + 1);
  suma[0] = 0;
  sumb[0] = 0;
  rep(i, n) { suma[i + 1] = suma[i] + a[i]; }
  rep(i, m) { sumb[i + 1] = sumb[i] + b[i]; }
  ll total = 0;
  for (ll i = 0; i <= n; i++) {
    ll rem = k - suma[i];
    if (rem < 0)
      continue;
    ll l = lower_bound(sumb.begin(), sumb.end(), rem) - sumb.begin();
    if (l > m || sumb[l] > rem)
      l--;
    total = max(total, i + l);
  }
  cout << total << nl;
  auto end = chrono::high_resolution_clock::now();
  TIME(start, end);
  return 0;
}

Fixed submission:
#include <bits/stdc++.h>
#include <ext/pb_ds/assoc_container.hpp>
#include <ext/pb_ds/tree_policy.hpp>

using namespace __gnu_pbds;
using namespace std;

#pragma GCC optimize("Ofast")
#pragma GCC target("avx,avx2,fma")
#pragma GCC optimization("unroll-loops")

#define fast                                                                   \
  ios_base::sync_with_stdio(false);                                            \
  cin.tie(NULL);                                                               \
  cout.tie(NULL);
#define ll long long int
#define ull unsigned long long
#define ld long double

#define mod 1000000007
#define EULER 2.7182818284
#define INF 1000000000

#define pb push_back
#define ins insert
#define IT iterator
#define PQ priority_queue
#define nl "\n"
#define fi first
#define se second
#define maxe max_element
#define mine min_element
#define er erase
#define lb lower_bound
#define ub upper_bound

#define vi vector<int>
#define vll vector<ll>
#define vb vector<bool>
#define pi pair<int, int>
#define pll pair<ll, ll>
#define all(v) v.begin(), v.end()

#define mem(v, i)                                                              \
  memset(                                                                      \
      v, i,                                                                    \
      sizeof(                                                                  \
          v)) // v is array. To set all elements to 0 or -1 only. mem(arr,0);

#define repab(i, a, b) for (int i = (a); i <= (b); i++)
#define reprab(i, a, b) for (int i = (a); i >= (b); i--)
#define repll(i, a, b) for (ll i = (a); i <= (b); i++)
#define rep(i, n) for (int i = (0); i < (n); i++)
#define repr(i, n) for (int i = (n); i >= 0; i--)
#define bs bitset
#define bpc(a) __builtin_popcount(a)
#define tc                                                                     \
  int t;                                                                       \
  cin >> t;                                                                    \
  while (t--)
template <typename T> void TIME(T start, T end) {
#ifndef ONLINE_JUDGE
  double time_taken =
      chrono::duration_cast<chrono::nanoseconds>(end - start).count();
  time_taken *= 1e-9;
  cout << "\nExecuted in: " << fixed << time_taken << setprecision(9);
  cout << " sec";
#endif
}

int dx[] = {1, -1, 0, 0};
int dy[] = {0, 0, 1, -1};

ll max(ll a, ll b) {
  if (a > b)
    return a;
  return b;
}
ll min(ll a, ll b) {
  if (a < b)
    return a;
  return b;
}

ll mypow(ll a, ll b) {
  ll res = 1;
  while (b > 0) {
    if (b & 1)
      res = res * a;
    a = a * a;
    b >>= 1;
  }
  return res;
}
ll gcd(ll a, ll b) {
  if (b == 0)
    return a;
  return gcd(b, a % b);
}
//..............................!!!!!!Get ready to
//fight!!!!!!............................

int main() {
  auto start = chrono::high_resolution_clock::now();
  fast ll n, m, k;
  cin >> n >> m >> k;
  vll a(n + 1), b(m + 1);
  rep(i, n) cin >> a[i];
  rep(i, m) cin >> b[i];
  vll suma(n + 1), sumb(m + 1);
  suma[0] = 0;
  sumb[0] = 0;
  rep(i, n) { suma[i + 1] = suma[i] + a[i]; }
  rep(i, m) { sumb[i + 1] = sumb[i] + b[i]; }
  ll total = 0;
  for (ll i = 0; i <= n; i++) {
    ll rem = k - suma[i];
    if (rem < 0)
      continue;
    ll l = lower_bound(sumb.begin(), sumb.end(), rem) - sumb.begin();
    if (l > m || sumb[l] > rem)
      l--;
    total = max(total, i + l);
  }
  cout << total << nl;
  auto end = chrono::high_resolution_clock::now();
  TIME(start, end);
  return 0;
}