#include <iostream>
#include <fstream>

using namespace std;
 
ifstream fin("deque.in");
ofstream fout("deque.out");

int f,b,n, k, a[5000001], Deque[5000001],i;
long long s=0;
int main()
{
    fin>>n>>k;
    for (i = 1; i <= n; i++)
       fin>>a[i];
    f = 1; b = 0;
    for (i = 1; i <= n; i++)
    {
        while (f <= b && a[i] <= a[Deque[b]])
            b--;
        Deque[++b] = i;
 
        if (Deque[f] == i-k)
            f++;
 
        if (i >= k)
            s += a[Deque[f]];
    }
 
    fout<<s;
 
    return 0;
}