#include<bits/stdc++.h>
using namespace std;
int n,a,m,s[200000050],b[200000050],sum;
int main(){
	int q=1,xiao=1000;
	cin>>n>>m;
	for(int i=1;i<=n;i++){
		cin>>a;
		s[i]=a;
	}
	for(int i=1;i<=n-m+1;i++){
		for(int j=q;j<m+q;j++){
			sum+=s[j];
		}
		b[i]=sum;
		if(b[i]<xiao) xiao=b[i];
		sum=0;
		q++;
	}
	cout<<xiao<<"\n";
    return 0;
}