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

using namespace std;

ifstream fin("deque.in");
ofstream fout("deque.out");

deque<long long> l;


int main()
{
    long long n,k,a[50001],s=0;
    fin>>n>>k;
    for(int i=1;i<=n;i++)
    {
        fin>>a[i];
        if(!l.empty())
            while(a[l.front()]>a[i])
            {
                l.pop_front();
            }
        l.push_front(i);
        if((i-k)==l.back())
            l.pop_back();
        if(i>=3)
            s+=a[l.back()];
    }
    fout<<s;
    return 0;
}