#include <bits/stdc++.h>

using namespace std;

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

void usain_bolt()
{
    ios::sync_with_stdio(false);
    fin.tie(0);
}

const int N = 5e6 + 5;

int dq[N], a[N];

int main()
{
    usain_bolt();

    int n, k, l = 0, r = 1;

    long long sum = 0;

    fin >> n >> k;
    for(int i = 1; i <= n; ++i) fin >> a[i];
    for(int i = 1; i <= n; ++i) {
        while(l >= r && a[i] <= a[dq[l]]) --l;
        dq[++l] = i;
        if(dq[r] == i - k) ++r;
        if(i >= k) sum += 1LL * a[dq[r]];
    }
    fout << sum;
    return 0;
}