#include <iostream>
#include <fstream>
#include <deque>
using namespace std;
int numere[5000001];
int main()
{
    ifstream intrare("deque.in");
    ofstream iesire("deque.out");
    int n,i,k;
    long long suma=0;
    deque<int> coada;
    intrare>>n;
    intrare>>k;
    for (i=1;i<=n;i++)
    {
        intrare>>numere[i];
        while (!coada.empty()&&numere[coada.back()]>numere[i]){coada.pop_back();}
        coada.push_back(i);
        if(i-coada.front()==k) coada.pop_front();
        if(i>=k) suma=suma+numere[coada.front()];
    }
    iesire<<suma<<"\n";
}