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

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

const int MAX=5e6;
int n,k,v[MAX+5],i;
long long sol;
deque <int> dq;
int main()
{
    fin>>n>>k;
    for (i=1; i<=n; i++)
        fin>>v[i];

    for (i=1; i<=k-1; i++)
    {
        while (!dq.empty() && v[i]<=v[dq.back()])
            dq.pop_back();

        dq.push_back(i);
    }

    for (i=k; i<=n; i++)
    {
        while (!dq.empty() && v[i]<=v[dq.back()])
            dq.pop_back();

        dq.push_back(i);

        while (!dq.empty() && dq.front()<=i-k)
            dq.pop_front();

        sol+=v[dq.front()];
    }

    fout<<sol;
    return 0;
}