#include<iostream>
#include<string.h>
#include<cmath>
using namespace std;
int n,m;
int a[3000];
int main(){
	cin>>n>>m;
	int k=0;
	int sum=0,sum1=0;
	int minn=114514;
	for(int i=0;i<n;i++){
		cin>>a[i];
	}
	for(int i=0;i<m;i++){
		sum+=a[i];
	}
	for(int i=m;i<n;i++){
		minn=min(sum,minn);
		sum-=a[i-m];sum+=a[i];
	}
	if(minn==114514){
		cout<<0;
		return 0;
	}
	cout<<minn;
	return 0;
}