#include <iostream>
#include <fstream>
#include <deque>
using namespace std;
ifstream fin("deque.in");
ofstream fout("deque.out");
int n,k;
int a[5000005];
long long ts=0;
deque<int> dq;
int main()
{
    fin>>n>>k;
    for(int i=1;i<=n;i++)
    {
        fin>>a[i];
        //cout<<a[i]<<endl;
        while(!dq.empty() && a[dq.back()]>a[i])
        {
            dq.pop_back();
        }
        dq.push_back(i);
        if(dq.front()<=i-k)
        {
            dq.pop_front();
        }
        if(i>=k)
        {
            //cout<<dq.front()<<endl;
            ts+=a[dq.front()];
        }
    }
    fout<<ts;
    return 0;
}