#include <bits/stdc++.h>

using namespace std;

long long n, k, ans;
deque<pair<long long, int>> sk;

int main() {
    ifstream cin("deque.in");
    ofstream cout("deque.out");
    cin >> n >> k;
    for(int i = 1; i <= n; i++) {
        long long x;
        cin >> x;
        if(i >= k && x <= sk.back().first) {
            while(x <= sk.back().first)
                sk.pop_back();
        }
        sk.push_back({x, i});
        if(sk.front().second == i - k)
            sk.pop_front();
        if(i >= k)
            ans += sk.front().first;
    }
    cout << ans;
    return 0;
}