#include<bits/stdc++.h>
using namespace std;
int main(){
	int n,m;
	cin>>n>>m;
	int a[33000],summin=300000;
	a[-1]=300000;
	a[-2]=300000;
	for(int i=0;i<n;i++){
		cin>>a[i];
	}
	for(int i=0;i<n;i++){
		int sum=0;
		for(int j=0;j<m&&i+m-1<n;j++){
			sum+=a[i+j];
		}
		if(sum<summin&&sum!=0){
			summin=sum;
		}
	}
	cout<<summin<<endl;
	return 0;
}