Language: C++

// "for if God is with them who can be against them."
#include<bits/stdc++.h>
using namespace std;
typedef long long ll;
typedef vector<int> vi;
typedef pair<int, int> pii;
#define IOS ios_base::sync_with_stdio(false);cin.tie(0);
#define F first
#define S second
#define PB push_back
#define MP make_pair
#define endl '\n'
#define REP(i,a,b) for(int i=a;i<=b;i++)
#define all(a) a.begin(),a.end()
#define watch(x) cout << (#x) << " is " << (x) << endl
void solve() {
	ll n, m, k;
	cin >> n >> m >> k;
	vector<ll>a(n );
	vector<ll>b(m );
	for (int i = 0; i < n; i++) {
		cin >> a[i];
	}
	for (int i = 0; i < m; i++) {
		cin >> b[i];
	}
	ll ans = 0, res = 0;
	vector<ll>prea(n);
	vector<ll>preb(m);
	ll ind = -1;
	prea[0] = a[0];
	if (prea[0] <= k) {
		ans++;
		ind = 0;
	}
	preb[0] = b[0];
	for (int i = 1; i < n; i++) {
		prea[i] = a[i] + prea[i - 1];
		if (prea[i] <= k) {
			//cout << prea[i] << endl;
			ans++;
			ind = i;
		}
	}
	REP(i, 1, m - 1) {
		preb[i] = b[i] + preb[i - 1];
	}
	if (ind == -1) {
		auto it = upper_bound(all(preb), k);
		if (it != preb.end()) {
			cout << (it - preb.begin());
		}
		else
			cout << m;
		return;
	}
	//cout << ans << endl;
	res = max(res, ans);
	for (int i = ind; i >= 0 and ans >= 0; i--) {
		auto it = upper_bound(all(preb), k - prea[ind]);
		if (it != preb.end()) {
			res = max(res, ans + it - preb.begin());
		}
		else
			res = max(res, ans + m);
		ans--;
	}
	cout << res;
}
int main() {
#ifndef ONLINE_JUDGE
	freopen("input1.txt", "r", stdin);
	freopen("output1.txt", "w", stdout);
#endif
	IOS;
	int t = 1;
	//cin >> t;
	while (t--) {
		solve();
	}


#ifndef ONLINE_JUDGE
	cout << "\nTime Elapsed: " << 1.0 * clock() / CLOCKS_PER_SEC << " sec\n";
#endif
	return 0;
}

Compiler output:
a.cc: In function 'void solve()':
a.cc:62:34: error: no matching function for call to 'max(ll&, __gnu_cxx::__normal_iterator<long long int*, std::vector<long long int> >::difference_type)'
   62 |                         res = max(res, ans + it - preb.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:2:
/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:62:34: note:   deduced conflicting types for parameter 'const _Tp' ('long long int' and '__gnu_cxx::__normal_iterator<long long int*, std::vector<long long int> >::difference_type' {aka 'long int'})
   62 |                         res = max(res, ans + it - preb.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:62:34: note:   mismatched types 'std::initializer_list<_Tp>' and 'long long int'
   62 |                         res = max(res, ans + it - preb.begin());
      |                               ~~~^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~