#include <iostream>
#include <deque>
#include <fstream>
using namespace std;
ifstream fin ("deque.in");
ofstream fout ("deque.out");
deque <int > d;
long long int a[5000001],n,k,s = 0;
void citire()
{
    fin >> n >> k;
    for( int i = 0; i < n; i++)
    {
        fin >> a[i];
        while(!d.empty() && a[i] <= a[d.back()])
            d.pop_back();
        d.push_back(i);
        while( d.front() < i - k + 1)
            d.pop_front();
        if(i >= k - 1)
            s += a[d.front()];

    }

}

int main()
{
    citire();
    fout << s;
    return 0;
}