#include <iostream>
#include <fstream>
using namespace std;

int main()
{
    ifstream in("deque.in");
    ofstream out("deque.out");
    int dr=-1,st=0;
    int n,k,v[50000],dq[5000],sum=0;
    in>>n>>k;
    for(int i=0;i<n;i++)
    {

        in>>v[i];
        if(st<=dr && dq[st]==i-k)
        {
            st++;
        }
        while(st<=dr && v[i]<=v[dq[dr]])
        {
            dr--;
        }
        dq[++dr]=i;
        if(i>=k-1)
        {
            sum+=v[dq[st]];
        }
    }
    out<<sum;
    return 0;
}