#include<iostream>
#include<iomanip>
#include<cstdio>
#include<cstring>
#include<cmath>
using namespace std;
int main(){
	int n,m;
	int a[23333];
	cin>>n>>m;
	for(int i = 1;i <= n;++i){
		cin>>a[i];
	}
	int min = 0x3f3f3f;
	int sum = 0;
	for(int i = 1;i <= n;++i){
		for(int j = i;j < i + m;++j){
			sum += a[j];
		}
		if(i + m > n){
			break;
		}
		//cout<<sum<<" ";
		if(sum < min){
			min = sum;
		}
		sum = 0;
	}
	cout<<min;
	return 0;
}