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

using namespace std;

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

deque<int> deq;
int a[5000001],i,n,k;
long long s;

int main()
{
    in>>n>>k;
    for(i=1;i<=n;i++)
    {
        in>>a[i];
        while(!deq.empty() && a[i]<a[deq.back()])
            deq.pop_back();
        deq.push_back(i);

        if(deq.front()==i-k)
            deq.pop_front();

        if(i>=k)
            s+=a[deq.front()];
    }
    out<<s;
    return 0;
}