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

int main()
{
    deque <int> dq;
    ifstream in("deque.in");
    ofstream out("deque.out");
    int n, k;
    long long int suma=0;
    int v[5000000];
    in >> n >> k;

    for(int i=0 ; i<n ; i++)
    {
        in >> v[i];
        if(!dq.empty() && dq.front() == i-k)
        {
            dq.pop_front();
        }

        while(!dq.empty() && v[i] <= v[dq.back()])
        {
            dq.pop_back();
        }
        dq.push_back(i);
        if(i >= k-1)
        {
            suma+=v[dq.front()];
        }
    }
    out<<suma;

    in.close();
    out.close();
    return 0;
}