#include <iostream>

#include <deque>
#include <fstream>
using namespace std;
deque <int> s;
int n,k,i,x[5000001];
long long su=0;
int main()
{   ifstream f("deque.in");
    ofstream g("deque.out");
    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;
}