#include <iostream>
#include <fstream>

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

int a[5000001], b[5000001], n, k, p, u, i;
long long s;

int main()
{
    f>> n >> k;

    for(i = 1; i <= n; i++)
        f>>a[i];

    p = 1;

    for(i = 1; i <= n; i++)
    {
        while(p <= u && a[i] < a[b[u]])
            u--;
        b[++u] = i;
        if(b[p] == i - k)
            p++;
        if(i >= k)
            s = s + a[b[p]];
    }

    g<< s;

    return 0;
}