#include <iostream>
#include <fstream>
using namespace std;
ifstream in("deque.in");
ofstream out("deque.out");
int main()
{
    long long n,v[5000000],coada[5000000],mini=-10000000,k;
    int sf=0,inc=0,i,s;
    coada[0]=mini;
    cin>>n>>k;
    for(i=1;i<=n;i++)
    {
        cin>>v[i];
        if(i<k)
        {
            while(v[i]<v[coada[sf]] && sf>=inc)
                sf--;
            coada[sf++]=i;
        }
        else
        {
            if(i-k>=coada[inc])
                inc++;
                while(v[i]<v[coada[sf]] && sf>=inc)
                    sf--;
                coada[sf++]=i;
                s=s+v[coada[inc]];
        }
    }
    cout<<s;
    return 0;
}