#include <iostream>
#include <fstream>

using namespace std;

int v[5000001], mn[5000001];

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

int main()
{
    int n, k, i, a, g, x;
    in >> n >> k;
    g = x = 0;
    mn[g+1] = 10000001;
    mn[g] = -10000001;
    for ( i = a = 1; i <= k; i++ ) { // Citesc pana la k
        in >> v[i];
        while ( v[i] < mn[a] ) { // Creez vectorul cu minime
            a--;
        }
        a++;
        mn[a] = v[i];
    }
    x = mn[g+1];
    for ( i = k+1; i <= n; i++ ) {
        in >> v[i];
        if ( mn[g+1] == v[i-k] ) {
            g++;
            mn[g] = -10000001;
        }
        while ( v[i] < mn[a] ) {
            a--;
        }
        a++;
        mn[a] = v[i];
        x += mn[g+1];
    }
    out << x;
    return 0;
}