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

using namespace std;

deque <int> a;
int vect[5000000];

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

    int n, k, x;
    long long s=0;

    f>>n>>k;
    for(int i=1; i<=n; i++)
    {
        f>>x;
        vect[i]=x;

        while(!a.empty() && x<=vect[a.back()])
            a.pop_back();
        a.push_back(i);

        if(i>=k)
        {
            while(i-a.front() >= k)
                a.pop_front();
            s += vect[a.front()];
        }
    }
    return s;
}

int main()
{
    cout<<rez();
    return 0;
}