#include <iostream>
#include <vector>
#include <deque>
#include <fstream>
using namespace std;

int main()
{   fstream f,g;
    f.open("deque.in",ios::in);
    g.open("deque.out",ios::out);
    deque <int> s;
    int n,k,i,x[50000001];
    long long su=0;
    f>>n>>k;
    for(i=0;i<n;i++)
        f>>x[i];
            for(i=0;i<n;i++){

        if(s.empty()){
            s.push_back(x[i]);
        }
        else {
            while(x[i]<=s.back() && !s.empty())
                s.pop_back();
            s.push_back(x[i]);
        }
        if((s.front())==x[i+1-k])
        {

            su+=s.front();
            s.pop_front();
        }
        else if(i+1-k>=0){

            su+=s.front();}

    }
g<<su;
return 0;
}