#include <iostream>
#include <fstream>
using namespace std;
ifstream f ("deque.in");
ofstream g ("deque.out");
long long n, k, i, j, minim, suma;
int main()
{
    f>>n>>k;
    long long v[n+1];
    for(i = 1; i <= n; i++)
        f >> v[i];
    for(i = 1; i <= n - k; i++)
    {
        minim = v[i];
        for(j = i+1; j < i + k; j++)
            if(v[j] < minim) minim = v[j];
        suma += minim;
    }
    g << suma;
    return 0;
}