#include <bits/stdc++.h>
#define MAXSZ 5000000
#define LL long long

using namespace std;

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

int main() {
    int n, k;
    LL sum = 0;
    deque<pair<LL, int>> mins;

    fin >> n >> k;
    for (int i = 0; i < n; i++) {
        LL x;
        fin >> x;
        while (!mins.empty() && mins.back().first >= x)
            mins.pop_back();
        mins.emplace_back(x, i);
        if (mins.front().second == i - k)
            mins.pop_front();
        if (i >= k - 1)
            sum += mins.front().first;
    }

    fout << sum;
    return 0;
}