#include <iostream>
#include <fstream>

using namespace std;

ifstream fin("deque.in");
ofstream fout("deque.out");

int n, v[500000], s, x, q, minim = 99999999;

int main()
{
    fin >> n >> q;
    for(int i=1; i<=n; i++)
        fin>>v[i];
    for(int i=1; i<=n - q + 1; i++)
    {
        for(int j = i; j<=i + q - 1; j++)
        {
            if(minim > v[j])
                minim = v[j];
        }
        s = s + minim;
        minim = 999999999;
    }
    fout<<s;
}