Language: C++

#include <bits/stdc++.h>
#define rep(i,n) for(int i = 0; i < n; i++)
using namespace std;
typedef long long ll;
typedef pair<int,int> P;
const int MAX_N = 200005;
ll A[MAX_N],B[MAX_N];
vector<ll> sumA,sumB;

int main()
{
	ll N,M,K;
	cin >> N >> M >> K;
	sumA.push_back(0);
	rep(i,N)
	{
		cin >> A[i];
		sumA.push_back(sumA[i] + A[i]);
	}
	sumB.push_back(0);
	rep(i,M)
	{
		cin >> B[i];
		sumB.push_back(sumB[i] + B[i]);
	}
	int ans = 0;
	for (int i = 0; i <= N; ++i)
	{
		if (sumA[i] > K) break;
		ans = max(ans,i+(upper_bound(sumB.begin(), sumB.end(), K - sumA[i]) - sumB.begin() - 1));
		//cout << ans << " ";
	}
	cout << ans << endl;
	return 0;
}

Compiler output:
a.cc: In function 'int main()':
a.cc:30:26: error: no matching function for call to 'max(int&, __gnu_cxx::__normal_iterator<long long int*, std::vector<long long int> >::difference_type)'
   30 |                 ans = max(ans,i+(upper_bound(sumB.begin(), sumB.end(), K - sumA[i]) - sumB.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: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:30:26: 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'})
   30 |                 ans = max(ans,i+(upper_bound(sumB.begin(), sumB.end(), K - sumA[i]) - sumB.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:30:26: note:   mismatched types 'std::initializer_list<_Tp>' and 'int'
   30 |                 ans = max(ans,i+(upper_bound(sumB.begin(), sumB.end(), K - sumA[i]) - sumB.begin() - 1));
      |                       ~~~^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~