#include <iostream>
#include <fstream>

using namespace std;

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

int n, k, v[5000001], d[5000001], p = 1, u = 0;
long long s;

int main()
{
    in>>n>>k;
    for(int i = 1 ; i <= n; i++)
        in>>v[i];

    for(int i = 1; i <=n; i++)
    {
        while(p <= u && v[i] <= v[d[u]])
            u--;

        u++;
        d[u] = i;

        if (d[p] == i-k)
            p++;

        if (i >= k)
            s += v[d[p]];
    }
    out<<s;

    return 0;

}