#include <bits/stdc++.h>

using namespace std;

ifstream f("deque.in");
ofstream g("deque.out");

const int N = 5000005;

int v[N], Deq[N], i, st, dr, n, k;
long long s;

int main()
{
    f >> n >> k;
    st = 1;
    dr = 0;
    for(i = 1; i <= n; ++ i)
    {
        f >> v[i];
        while(st <= dr && v[i] <= v[Deq[dr]])
            dr --;
        Deq[++ dr] = i;
        while(Deq[st] <= i - k)
            st ++;
        if(i >= k)
            s = s + v[Deq[st]];
    }
    g << s;
    return 0;
}