#include <iostream>
#include <fstream>
#include <deque>

using namespace std;

deque <int>d;

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

int a[5000000],i,p,u,n,k;
long long s;

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

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

    for(i=1;i<=n;i++)
    {
        while(!d.empty() && a[i]<a[d[d.size()-1]])
            d.pop_back();
        d.push_back(i);
        if(i-k==d[0])
            d.pop_front();
        if(i>=k)
            s=s+a[d[0]];
    }

    g<<s;
    return 0;
}