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

using namespace std;

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

int n,k;
long long s=0,v[5000001];
deque<int> dq;

int main()
{
    fin>>n>>k;
    for(int i=1;i<=n;i++)
    {
        fin>>v[i];
    }
    for(int i=1;i<=n;i++)
    {
        if(!dq.empty()&&dq.front()<i-k+1)
            dq.pop_front();
        while(!dq.empty()&&v[dq.back()]>v[i])
        {
            dq.pop_back();
        }
        dq.push_back(i);
        if(i>=3)
            s+=v[dq.front()];
    }
    fout<<s;
}