#include <bits/stdc++.h>

using namespace std;

long long n, k, s, nmin = 10000000, v[5000001];
deque<int> dq;

int main() {
    //ifstream cin("alee.in");
    //ofstream cout("alee.out");
    cin >> n >> k;
    for(int i = 1; i <= n; i++)
        cin >> v[i];

    for(int i = 1; i <= n; i++) {
        while(!dq.empty() && v[i] <= v[dq.back()])
            dq.pop_back();
        dq.push_back(i);
        if(dq.front() == i - k)
            dq.pop_front();
        if(i >= k)
            s += v[dq.front()];
    }
    cout << s;
    return 0;
}