#include <iostream> //评测记录：https://www.luogu.com.cn/record/164839082
using namespace std;
int n,m,a[1111],sum=0,minn=114514;
int main(){
    cin>>n>>m;
    for(int i=0;i<n;i++) cin>>a[i];
    for(int i=0;i<=n-m;i++){
        for(int j=i;j<=i+m;j++) sum+=a[j];
        if(sum<minn) minn=sum;
        sum=0;
    }
    cout<<minn;
    return 0;
}