#include <bits/stdc++.h>
using namespace std;

int main () {
    freopen("deque.in", "r", stdin);
    freopen("deque.out", "w", stdout);

    ios::sync_with_stdio(false);
    cin.tie(nullptr);
    cout.tie(nullptr);

    int n, k;
    cin >> n >> k;

    deque <pair <int, int>> DQ;
    long long ans = 0;

    int i, x;
    for (i = 1; i <= n; i++) {
        cin >> x;
        while (!DQ.empty() && DQ.back().second >= x)
            DQ.pop_back();
        
        DQ.emplace_back(i, x);
        if (DQ.front().first == i - k)
            DQ.pop_front();
        
        if (i >= k)
            ans += DQ.front().second;
    }

    cout << ans;
    return 0;
}