#include<bits/stdc++.h>
using namespace std;

int main(){
	int n,m;
	scanf("%d%d",&n,&m);
	int h[n];
	for(int k=0;k<n;k++){
		scanf("%d",&h[k]);
	}
	int sum,summin;
	for(int i=0;i<n-m+1;i++){
		sum=0;
		for(int j=i;j<i+m;j++){
			sum+=h[j];
		}
		if(i==1){
			summin=sum;
		}
		if(sum<summin){
			summin=sum;
		}
		//cout<<endl<<"第"<<i<<"轮，sum="<<sum<<"，summax="<<summax;
	}
	printf("%d",summin);
	
	return 0;
}