#include<bits/stdc++.h>
#define in f
#define out g
using namespace std;

ifstream f ("deque.in");
ofstream g ("deque.out");


int n;
int k;
int aux;
int s;
int v[5000010];

int main() {

    in >> n;
    in >> k;

    for(int i = 1; i <= n; i++) {
        in >> v[i];
    }
    for(int i = 1; i <= n - k + 1; i++) {
        aux = v[i];
        for(int j = i + 1; j < i + k ; j++) {
            aux = min(aux, v[j]);
        }
        s = s + aux;
    }
    out << s;

}