/*
AM un sir cu N elem vr sa iau subsiruri de lg K si sa
iau minimul subsirului si sa l adun la o suma;
*/

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

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

const int MAX_VAL = 10000000;

#define VI vector<int>

void brute();

VI sir;
int N, K;

int main() {
    brute();
}

void brute() {
    fin >> N >> K;
    sir = VI(N + 1);
    for (int i = 0; i < N; ++i) {
        fin >> sir[i];
    }
    long long suma = 0;
    for (int i = 0; i <= N - K; ++i) {
        int minSub = MAX_VAL;
        for (int j = 0; j < K; ++j) {
            minSub = min(sir[i + j], minSub);
        }
        //fout << minSub << ' ';
        suma += minSub;
    }
    fout << suma;
}