#include<iostream>
#include<cstring>
using namespace std;
int main()
{
	int n,m,i,s = 0,min = 300001;
	cin >> n >> m;
	int a[10050];
	memset(a,0,sizeof(a));
	for(i = 0;i < n;i ++)
	cin >> a[i];
	for(i = 0;i < m;i ++)
	s += a[i];//前m个连续求和
	for(i = 0;i + m < n;i ++)
	{
		if(i == 0)
		{
			if(s < min)
			min = s;
		}
		s = s - a[i] + a[i + m];//去掉最前一个加上往后一个
		if(s < min)
			min = s;
	}
	cout << min;
	return 0;
}