#include <iostream>
#include <fstream>


using namespace std;

long long s;
int i, p, u, v[5000100], d[5000100], n, k;

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

    f>>n>>k;
    for(i = 1; i <= n; i++)
        f>>v[i];
    p = 1;
    u = 1;
    d[p] = 1;
    for(i = 2; i <= n; i++)
    {
        while(v[i] <= v[d[u]] && p <= u)
            u--;
        d[++u] = i;
        if(i - d[p] == k)
            p++;
        if(i >= k)
            s += v[d[p]];
    }
    g<<s;
    return 0;
}