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

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

int n,k,i,a[5000001];
long long s;
deque<int>deck;
int main()
{
    f>>n>>k;
    for(i=1;i<=n;i++)
    {
        f>>a[i];
        while(!deck.empty() && deck.back()>a[i])
        deck.pop_back();
        deck.push_back(a[i]);
        if(i>=k)
        s=s + deck.front();
    }
    g << s;
    return 0;
}