#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];

long long sum = 0;

int main()
{
    usain_bolt();

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