#include <bits/stdc++.h>
using namespace std;
ifstream f("deque.in");
ofstream g("deque.out");

deque <pair<int, int>> dq;
vector <int> rez;

int main()
{
    int n, k, x;
    long long suma = 0;
    f >> n >> k;
    for(int i=1; i<=n; i++)
    {
        f >> x;

        while(!dq.empty() && dq.back().first >= x)
            dq.pop_back();
        while(!dq.empty() && i - dq.front().second + 1 > k)
            dq.pop_front();

        dq.push_back(make_pair(x, i));

        if(i >= k && !dq.empty())
            suma += dq.front().first;
    }
    g << suma;
}