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

ifstream fin("deque.in");
ofstream fout("deque.out");
deque <int> minimum;
ll result;
int v[5000000];

int main() {
    int n, k;

    fin >> n >> k;
    for (int i = 1; i <= n; i++) {
       fin >> v[i];

        while (!minimum.empty() && v[i] <= v[minimum.back()])
            minimum.pop_back();
        minimum.push_back(i);

        if (i - k  == minimum.front())
            minimum.pop_front();

        if (i >= k)
            result += v[minimum.front()];
    }

    fout << result;

    return 0;
}