#include <iostream>
using namespace std;
int main()
{
    int n,m,sum=0,min_s=1<<30;
    cin>>n>>m;
    int a[n+1];
    for(int i=1;i<=n;i++)
    {
        cin>>a[i];
    }
    for(int i=1;i<=n-m;i++)
    {
        sum = 0;
        for(int j=1;j<=m;j++)
        {
            sum += a[i+j];
        }
        if(sum<min_s)min_s = sum;
    }
    cout<<min_s<<endl;
    return 0;
}