#include <bits/stdc++.h>
using namespace std;
int a[3005],s[10000];
int main () {
	int n,m;
	scanf ("%d %d",&n,&m);
	for (int i=1;i<=n;i++){
		scanf ("%d",a+i);
	}
	for (int i=1;i<=n;i++){
		for (int j=i,js=1;js<=m;js++,j++){
			s[i]+=a[j];
		}
	}
	sort (s,s+n);
	printf ("%d",s[1]);
	return 0;
}