#include <bits/stdc++.h>

using namespace std;

int n, k;
int dq[5000000];
int v[5000000];
long long sum = 0;

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

int main()
{
    fin >> n >> k;
    for(int i = 1; i <= n; i ++)
    {
        fin >> v[i];
    }
    int st = 0, dr = -1;
    for(int i = 1; i <= n; i ++)
    {
        if(st <= dr && dq[st] == i - k)
        {
            st++;
        }

        while(st <= dr && v[dq[dr]] >= v[i])
            dr--;

        dq[++dr] = i;

        if(i >= k)
            sum = sum + v[dq[st]];
    }
    fout << sum << '\n';
}