#include <bits/stdc++.h>
using namespace std;
int n,m,s,minn = 1e9;
int a[10005];
int main(){
    cin >> n >> m;
    if(n == 0 || m == 0){
    	cout << 0;
    	return 0;
	}
    for(int i = 0;i < n;i++) cin >> a[i];
    for(int i = 0;i < n - m - 1;i++){
		int t = 0;
    	s = 0;
    	for(int j = i;t < m;t++,j++){
    		s += a[j];
		}
		minn = min(minn,s);
	}
    cout << minn;
}