#include <iostream>
#include <fstream>
using namespace std;
ifstream fin("deque.in");
ofstream fout("deque.out");
int v[5000000];
int a[5000000];
int main() {
    int N, K, i;
    fin >> N >> K;
    long int sum = 0, st = 1, dr = 0;
    for (i = 1; i <= N; i++) {
        fin >> v[i];
    }
    for (i = 1; i <= N; i++) {
        while (st <= dr && v[i] <= v[a[dr]])
            dr--;
        a[++dr] = i;
        if (a[st] == i - K)
            st++;
        if (i >= K)
            sum += v[a[st]];
    }

    fout << sum;
    fin.close();
    fout.close();
    return 0;
}