#include <bits/stdc++.h>

using namespace std;

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

int dq[5000005];
int v[50000005];
int n, k;
int ans;
int st, dr = -1;

int main()
{
    fin >> n >> k;
    for(int i = 1; i <= n; i ++)
    {
        fin >> v[i];
    }
    for(int i = 1; i <= n; i ++)
    {
        if(st <= dr && dq[st] == i - k)
        {
            st++;
        }
        while(st <= dr && v[i] <= v[dq[dr]])
            dr--;
        dq[++dr] = i;
        if(st <= dr && i >= k)
        {
            ans = ans + v[dq[st]];
        }
    }
    fout << ans << '\n';
}