#include <iostream>
#include <fstream>
using namespace std;

int main()
{
    int n, k;
    ifstream in("deque.in");
    ofstream out("deque.out");
    in >> n >> k;
    int v[n+3], suma = 0, x = 0;
    for(int i = 0; i < n; i++)
        in >> v[i];


    while(k + x <= n) {
        int minn = v[x];
        for(int i = x; i < k + x; i++)
            if(minn > v[i])
                minn = v[i];
        suma += minn;
        x++;
    }
    out << suma;
    return 0;
}