#include <bits/stdc++.h>
#define M 5000001

using namespace std;

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

int n, k, v[M], Front = 1, Back, dqueue[M];
long long sum;

int main() {
    in >> n >> k;
    for (int i = 1; i <= n; ++i)
        in >> v[i];

    for (int i = 1; i <= n; ++i) {
        while (Front <= Back && v[i] <= v[dqueue[Back]])
            --Back;

        dqueue[++Back] = i;

        if (dqueue[Front] == i - k)
            ++Front;

        if (i >= k)
            sum += v[dqueue[Front]];
    }

    out << sum;
    return 0;
}