Language: C++

#include <bits/stdc++.h> 
using namespace std; 
#define for_(i, s, e) for (int i = s; i < e; i++)
#define for__(i, s, e) for (ull i = s; i < e; i++)
#define SSTR(x) static_cast<std::ostringstream&>((std::ostringstream() << std::dec << x)).str()
typedef unsigned long long ull;
typedef long long ll;
typedef vector<int> vi;
typedef pair<int, int> ii;
#define endl "\n"


int main() {
    #ifndef ONLINE_JUDGE
	freopen("test.in", "r", stdin);
    #endif
    
    ios_base::sync_with_stdio(false);
    cin.tie(0);
    
    int n, m, k; cin >> n >> m >> k;
    vector<ll> a(n), b(m);
    for_(i, 0, n) cin >> a[i];
    for_(i, 0, m) cin >> b[i];
    for_(i, 1, n) a[i] += a[i-1];
    for_(i, 1, m) b[i] += b[i-1];

    int ans = upper_bound(b.begin(), b.end(), k) - b.begin();
    for_(i, 0, n) {
        if (a[i] > k) break;
        ans = max(ans, i + 1 + upper_bound(b.begin(), b.end(), k - a[i]) - b.begin());
    }

    cout << ans << endl;
    

    return 0;
}

Compiler output:
a.cc: In function 'int main()':
a.cc:31:18: error: no matching function for call to 'max(int&, __gnu_cxx::__normal_iterator<long long int*, std::vector<long long int> >::difference_type)'
   31 |         ans = max(ans, i + 1 + upper_bound(b.begin(), b.end(), k - a[i]) - b.begin());
      |               ~~~^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
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:1:
/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:31:18: 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'})
   31 |         ans = max(ans, i + 1 + upper_bound(b.begin(), b.end(), k - a[i]) - b.begin());
      |               ~~~^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
/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:31:18: note:   mismatched types 'std::initializer_list<_Tp>' and 'int'
   31 |         ans = max(ans, i + 1 + upper_bound(b.begin(), b.end(), k - a[i]) - b.begin());
      |               ~~~^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~