#include <iostream>
using namespace std;

void Heart()
{
    int n = 0 , m = 0 ;
    cin >> n >> m ;
    int arr[n] ;
    int Min = 0 , Mintemp = 0 ;
    for ( int i = 0 ; i < n ; i++ )
    {
        cin >> arr[i];
    }
    for ( int i = 0 ; i < m ; i++ )
    {
        Min += arr[i] ;
    }
    for ( int i = 0 ; i < n - 2 ; i++ )
    {
        for ( int j = i ; j < m + i ; j++ )
        {
            Mintemp += arr[j] ;
        }
        if ( Mintemp < Min )
        {
            Min = Mintemp ;
        }
        Mintemp = 0 ;
    }
    cout << Min << endl ;
}

int main(int argc, const char * argv[]) {

    Heart() ;
    
    return 0;
}