能帮我看一下这串代码有什么问题吗？

#include<bits/stdc++.h>
using namespace std;
#define ll long long
ll n, m, c, maxval, ansx, ansy;
ll a[1001][1001], s[1001][1001];
ll get_fun(int x1,int y1,int x2,int y2) {
	return s[x2][y2] + s[x1 - 1][y1 - 1] - s[x2][y1 - 1] - s[x1 - 1][y2];
}
int main(){
	cin >> n >> m >> c;
	for(int i = 1; i <= n; i++) {
		for(int j = 1; j <= m; j++) {
			cin >> a[i][j];
			s[i][j] = s[i][j - 1] + s[i - 1][j] - s[i - 1][j - 1] + a[i][j];
		}
	}
	for(int i = 1; i <= n; i++)
		for(int j = 1; j <= m; j++) {
			int k = i + c, l = j + c;
			if(maxval < get_fun(i, j, k, l)) {
				maxval = get_fun(i, j, k, l);
				ansx = i;
				ansy = j;
			}
		}
	cout << ansx << ' ' << ansy;
	return 0;
}