#include <iostream>
#include <fstream>
#include <deque>
#define NMAX 5000001
using namespace std;
ifstream f("deque.in");
ofstream g("deque.out");
deque <int> dq;
int n,a[NMAX],i,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(!dq.empty() && a[i]<=a[dq.back()])
        {
            dq.pop_back();
        }
        dq.push_back(i);
        while(dq.front()<=i-k)
        {
            dq.pop_front();
        }
        if(i>=k)
        {
            s=s+a[dq.front()];
        }
    }
    g<<s;
    return 0;
}