#include <iostream>
#include <fstream>

using namespace std;

ifstream fin("deque.in");
ofstream  fout("deque.out");
int n, k, v[5000001], deque[5000001];
int main() {
    int p = 1, q = 0, i;
    long long suma = 0;
    fin >> n >> k;
    for(i = 1; i <= n; ++i)
        fin >> v[i];
    for(i = 1; i <= n; ++i) {
        while (p <= q && v[i] < v[deque[q]])
            q--;
        deque[++q] = i;
        if (deque[p] == i - k)
            p++;
        if (i >= k)
            suma += v[deque[p]];
    }
    fout << suma;
    return 0;
}