#include <iostream>
#include <fstream>

std::ifstream f("deque.in");
std::ofstream g("deque.out");
long long n, k, v[5000001];
int main() {
    f>>n>>k;
    for( long long i=0 ; i<n ; i++ )
        f>>v[i];

    long long sum=0, min;

    for( int i=0 ; i<n-k+1 ; i++ )
    {
        min = 10000001;
        for(int j=i ; j<i+k ; j++)
        {
            if(v[j] < min) min = v[j];
        }
        sum = sum + min;
    }
    g<<sum;

    return 0;
}