#include<iostream>

using namespace std;

int main()
{
    int n,l,a[3005],b[3002],minn=200000000;
    b[0]=0;
    cin>>n>>l;
    for(int i=1;i<=n;i++)
    {
        cin>>a[i];
        b[i]=b[i-1]+a[i];
        if(i>=l)if(b[i]-b[i-l]<minn)minn=b[i]-b[i-l];
    }
    cout<<minn;
    return 0;
}