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

using namespace std;

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

 deque <int> my_de;

long long v[5000001],n,k,i,suma;

int main()
{f>>n;f>>k;
 for(i=1;i<=n;i++)
 {      f>>v[i];
        while(!my_de.empty()&&v[my_de.back()]>=v[i])
          my_de.pop_back();
        my_de.push_back(i);
        if(my_de.front()==i-k)
          my_de.pop_front();
        if(i>=k)
          suma=suma+v[my_de.front()];
    }
    g<<suma;
    return 0;
}