RT，代码如下

#include<iostream>
#include<cstdio>
#include<queue>
using namespace std;
long long n, m, minn = 999999999, x, sum;
queue<long long> q;
int main()
{
	cin >> n >> m;
	for(int i = 1; i <= n; i++)
	{
		cin >> x;
		if(i <= m)
		{
			q.push(x);
			sum += x;
			if(i == m)
				minn = min(minn, sum);
		}
		else
		{
			sum -= q.front();
			q.pop();
			q.push(x);
			sum += x;
			minn = min(minn, sum);
		}
	}
	cout << minn;
	return 0;
}