Problem p02623 (C++)

Buggy submission (status: Runtime Error):
#ifndef LOCAL
#pragma GCC optimize("O3")
#endif
#include "bits/stdc++.h"
#include <ext/pb_ds/assoc_container.hpp> // Common file
#include <ext/pb_ds/detail/standard_policies.hpp>
#include <ext/pb_ds/tree_policy.hpp> // Including tree_order_statistics_node_update
using namespace std;
using namespace __gnu_pbds;
#define sim template <class c
#define int long long
#define ris return *this
#define dor > debug &operator<<
#define eni(x)                                                                 \
  sim > typename enable_if<sizeof dud<c>(0) x 1, debug &>::type operator<<(    \
            c i) {
sim > struct rge {
  c b, e;
};
sim > rge<c> range(c i, c j) { return rge<c>{i, j}; }
sim > auto dud(c *x) -> decltype(cerr << *x, 0);
sim > char dud(...);
struct debug {
#ifdef LOCAL
  ~debug() { cerr << '\n'; }
  eni(!=) cerr << boolalpha << i;
  ris;
} eni(==) ris << range(begin(i), end(i));
}
sim, class b dor(pair<b, c> d) {
  ris << "(" << d.first << ", " << d.second << ")";
}
sim dor(rge<c> d) {
  *this << "[";
  for (auto it = d.b; it != d.e; ++it)
    *this << ", " + 2 * (it == d.b) << *it;
  ris << "]";
}
#else
  sim dor(const c &) { ris; }
#endif
}
;
#define imie(...) " [" << #__VA_ARGS__ ": " << (__VA_ARGS__) << "] "
#define fastio                                                                 \
  ios_base::sync_with_stdio(false);                                            \
  cin.tie(0);
typedef tree<pair<int, int>, null_type, less<pair<int, int>>, rb_tree_tag,
             tree_order_statistics_node_update>
    ordered_set;
typedef long long ll;
const ll MOD = 1e9 + 7;
const ll N = 2e5 + 10;
const ll INF = 1e18 + 10;
signed main() {
  fastio int n, m, k;
  cin >> n >> m >> k;
  vector<int> A(n + 1), B(n + 1);
  for (int i = 0; i < n; i++) {
    int x;
    cin >> x;
    A[i + 1] = A[i] + x;
  }
  for (int i = 0; i < m; i++) {
    int x;
    cin >> x;
    B[i + 1] = B[i] + x;
  }
  int answer = 0;
  for (int i = 0; i < n + 1; i++) {
    if (A[i] <= k) {
      int target = k - A[i];
      int L = 0, R = m;
      int ans = -1;
      while (L <= R) {
        int mid = L + (R - L) / 2;
        if (B[mid] <= target) {
          ans = mid;
          L = mid + 1;
        } else
          R = mid - 1;
      }
      assert(ans != -1);
      answer = max(answer, i + ans);
    }
  }
  cout << answer << endl;
  return 0;
}

Fixed submission:
#ifndef LOCAL
#pragma GCC optimize("O3")
#endif
#include "bits/stdc++.h"
#include <ext/pb_ds/assoc_container.hpp> // Common file
#include <ext/pb_ds/detail/standard_policies.hpp>
#include <ext/pb_ds/tree_policy.hpp> // Including tree_order_statistics_node_update
using namespace std;
using namespace __gnu_pbds;
#define sim template <class c
#define int long long
#define ris return *this
#define dor > debug &operator<<
#define eni(x)                                                                 \
  sim > typename enable_if<sizeof dud<c>(0) x 1, debug &>::type operator<<(    \
            c i) {
sim > struct rge {
  c b, e;
};
sim > rge<c> range(c i, c j) { return rge<c>{i, j}; }
sim > auto dud(c *x) -> decltype(cerr << *x, 0);
sim > char dud(...);
struct debug {
#ifdef LOCAL
  ~debug() { cerr << '\n'; }
  eni(!=) cerr << boolalpha << i;
  ris;
} eni(==) ris << range(begin(i), end(i));
}
sim, class b dor(pair<b, c> d) {
  ris << "(" << d.first << ", " << d.second << ")";
}
sim dor(rge<c> d) {
  *this << "[";
  for (auto it = d.b; it != d.e; ++it)
    *this << ", " + 2 * (it == d.b) << *it;
  ris << "]";
}
#else
  sim dor(const c &) { ris; }
#endif
}
;
#define imie(...) " [" << #__VA_ARGS__ ": " << (__VA_ARGS__) << "] "
#define fastio                                                                 \
  ios_base::sync_with_stdio(false);                                            \
  cin.tie(0);
typedef tree<pair<int, int>, null_type, less<pair<int, int>>, rb_tree_tag,
             tree_order_statistics_node_update>
    ordered_set;
typedef long long ll;
const ll MOD = 1e9 + 7;
const ll N = 2e5 + 10;
const ll INF = 1e18 + 10;
signed main() {
  fastio int n, m, k;
  cin >> n >> m >> k;
  vector<int> A(n + 1), B(m + 1);
  for (int i = 0; i < n; i++) {
    int x;
    cin >> x;
    A[i + 1] = A[i] + x;
  }
  for (int i = 0; i < m; i++) {
    int x;
    cin >> x;
    B[i + 1] = B[i] + x;
  }
  int answer = 0;
  for (int i = 0; i < n + 1; i++) {
    if (A[i] <= k) {
      int target = k - A[i];
      int L = 0, R = m;
      int ans = -1;
      while (L <= R) {
        int mid = L + (R - L) / 2;
        if (B[mid] <= target) {
          ans = mid;
          L = mid + 1;
        } else
          R = mid - 1;
      }
      assert(ans != -1);
      answer = max(answer, i + ans);
    }
  }
  cout << answer << endl;
  return 0;
}