#include <iostream>
#include <fstream>
using namespace std;
ifstream fin("deque.in");
ofstream fout("deque.out");
int v[5000005],coada[5000005];
int main()
{
    int n,k,i,inc,s=0,sf;
    v[0]=-10000001;
    sf=0;
    inc=0;
    fin>>n>>k;
    for(i=1; i<=n; i++)
    {
        fin>>v[i];
        if(i<k)
        {
            while (inc<=sf && v[i]<v[coada[sf]])
                sf--;
            coada[++sf]=i;
        }
        else
        {
            if(i-k+1>coada[inc])
                inc++;
            while (inc<=sf && v[i]<v[coada[sf]])
                sf--;
            coada[++sf]=i;
            s=s+v[coada[inc]];
        }
    }
        fout<<s;
        return 0;

}