#include <stdio.h>
int main()
{
	int n,m,pain[3005],i,all=0,min=0,j,a=0;
	scanf("%d%d",&n,&m);
	for(i=0;i<n;i++)
	{
		scanf("%d",&pain[i]);
		if(i==m-1)
		{
			j=0;
			while(i-j>=0)
			{
				min+=pain[i-j];
				j++;
			}
		}
		else if(i>m-1)
		{
			all=min-pain[a]+pain[i];
			a++;
			if(min>all)
				min=all;
		}
	}
	printf("%d",min);
	return 0;
}