#include <bits/stdc++.h>

using namespace std;

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

deque <long long> dq,pos;
long long suma=0;
long long x,n,k;

int main()
{
    fin>>n>>k;
    for (int i=1;i<=n;i++)
    {
        fin>>x;
        while (x<dq.front() && !dq.empty())
        {
            dq.pop_front();
            pos.pop_front();
        }
        if (dq.empty() || x>dq.front())
            {
                dq.push_front(x);
                pos.push_front(i);
            }
        if (i>=k)
        {
            suma+=dq.back();
            if (i-k+1>=pos.back())
            {
                dq.pop_back();
                pos.pop_back();
            }
        }
    }
    fout<<suma;
    return 0;
}