Language: C++

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

#include <bits/stdc++.h>

using namespace std;

#define int long long
#define sz(a) (int) (a).size()
#define all(a) (a).begin(), (a).end()
#define x first
#define y second

signed main() {
    ios::sync_with_stdio(false);
    cin.tie(0), cout.tie(0);

    int n, m, x;
    cin >> n >> m >> x;
    vector<int> a(n + 1), b(m + 1);
    vector<int> s(m + 1);
    int ans = 0;
    for (int i = 1; i <= n; i++) {
        cin >> a[i];
    }
    for (int i = 1; i <= m; i++) {
        cin >> b[i];
        s[i] = s[i - 1] + b[i];
    }
    int sum = 0;
    for (int i = 0; i <= n; i++) {
        sum += a[i];
        if (x - sum < 0) break;
        auto it = max(0, upper_bound(all(s), x - sum) - s.begin() - 1);
        ans = max(ans, i + it);
    }
    cout << ans << '\n';
    return 0;
}

Compiler output:
a.cc: In function 'int main()':
a.cc:35:22: error: no matching function for call to 'max(int, __gnu_cxx::__normal_iterator<long long int*, std::vector<long long int> >::difference_type)'
   35 |         auto it = max(0, upper_bound(all(s), x - sum) - s.begin() - 1);
      |                   ~~~^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
In file included from /usr/include/c++/14/algorithm:60,
                 from /usr/include/x86_64-linux-gnu/c++/14/bits/stdc++.h:51,
                 from a.cc:5:
/usr/include/c++/14/bits/stl_algobase.h:257:5: note: candidate: 'template<class _Tp> constexpr const _Tp& std::max(const _Tp&, const _Tp&)'
  257 |     max(const _Tp& __a, const _Tp& __b)
      |     ^~~
/usr/include/c++/14/bits/stl_algobase.h:257:5: note:   template argument deduction/substitution failed:
a.cc:35:22: note:   deduced conflicting types for parameter 'const _Tp' ('int' and '__gnu_cxx::__normal_iterator<long long int*, std::vector<long long int> >::difference_type' {aka 'long int'})
   35 |         auto it = max(0, upper_bound(all(s), x - sum) - s.begin() - 1);
      |                   ~~~^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
/usr/include/c++/14/bits/stl_algobase.h:303:5: note: candidate: 'template<class _Tp, class _Compare> constexpr const _Tp& std::max(const _Tp&, const _Tp&, _Compare)'
  303 |     max(const _Tp& __a, const _Tp& __b, _Compare __comp)
      |     ^~~
/usr/include/c++/14/bits/stl_algobase.h:303:5: note:   candidate expects 3 arguments, 2 provided
In file included from /usr/include/c++/14/algorithm:61:
/usr/include/c++/14/bits/stl_algo.h:5706:5: note: candidate: 'template<class _Tp> constexpr _Tp std::max(initializer_list<_Tp>)'
 5706 |     max(initializer_list<_Tp> __l)
      |     ^~~
/usr/include/c++/14/bits/stl_algo.h:5706:5: note:   candidate expects 1 argument, 2 provided
/usr/include/c++/14/bits/stl_algo.h:5716:5: note: candidate: 'template<class _Tp, class _Compare> constexpr _Tp std::max(initializer_list<_Tp>, _Compare)'
 5716 |     max(initializer_list<_Tp> __l, _Compare __comp)
      |     ^~~
/usr/include/c++/14/bits/stl_algo.h:5716:5: note:   template argument deduction/substitution failed:
a.cc:35:22: note:   mismatched types 'std::initializer_list<_Tp>' and 'int'
   35 |         auto it = max(0, upper_bound(all(s), x - sum) - s.begin() - 1);
      |                   ~~~^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~