#include <fstream>
#include <iostream>

using namespace std;

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

const int NMAX = 5000000;
int deq[NMAX+1],
    a[NMAX+1];

int main()
{
    long long s = 0;
    int p = 1, u = 0,
        n, k;
    in >> n >> k;
    for(int i = 1; i <= n; i++)
        in >> a[i];
    for(int i = 1; i <= n; i++) {
        while(p <= u && a[i] <= a[deq[u]]) u--;
        deq[++u] = i;
        if(deq[p] == i-k) p++;
        if(i >= k)
            s += a[deq[p]];
    }
    out << s;
    return 0;
}