#include <fstream>

using namespace std;
ifstream in("deque.in");
ofstream out("deque.out");
int v[5000001],c[5000001];
int main()
{
    int n,k,sf=0,inc=0,i,s=0;
    v[0]=-10000007;
    in>>n>>k;
    for(i=1;i<=n;i++)
    {
        in>>v[i];
        if(i<k)
        {
            while(v[i]<v[c[sf]] && sf<=inc)
                sf--;
            c[++sf]=i;
        }
        else
        {
            if(i-k==c[inc])
                inc++;
            while(v[i]<v[c[0]] && sf<=inc)
                sf--;
            c[++sf]=i;
            s+=v[c[inc]];
        }
    }
    out<<s;
    return 0;
}