#include <bits/stdc++.h>
using namespace std;
int sum[100010],n,a[100010],k,ans;
int main()
{
	cin >> n >> k;
	for (int i = 1;i <= n;i++)
	{
		cin >> a[i];
		sum[i] = sum[i-1] + a[i];
	}
	for (int i = k;i <= n;i++)
	{
		ans = max(ans,sum[i]-sum[i-k]);
	}
	cout << ans;
	return 0;
}

然后发现第一篇题解是UKE