#include <iostream>
#include <fstream>
#include <deque>
using namespace std;
ifstream f("deque.in");
ofstream g("deque.out");

deque <int> d;
long long s;
int a[5000005],k,n,i;
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.back()])
            d.pop_back();
        d.push_back(i);
        if(d.front()==i-k)d.pop_front();
        if(i>=k)s+=a[d.front()];
    }
    g<<s;
    return 0;
}