/*
    "TLE is like the wind, always by my side"
    - Yasuo - 2022 -
*/
#include <bits/stdc++.h>
#pragma GCC optimize("Ofast")
#define debug(x) cerr << #x << " " << x << "\n"
#define debugs(x) cerr << #x << " " << x << " "

using namespace std;

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

deque <int> dq;
int v[5000001];

int main()
{
    ios_base::sync_with_stdio(false);
    cin.tie(0);
    cout.tie(0);
    int n,k,i;
    long long s=0;
    fin >> n >> k;
    for (i=1;i<=n;i++)
    {
        fin >> v[i];
        if (dq.front()==i-k)
            dq.pop_front();
        while (dq.size() && v[i]<=v[dq.back()])
        {
            dq.pop_back();
        }
        dq.push_back(i);
        if (i>=k)
        s+=v[dq.front()];
    }
    fout << s;
}