#include <fstream>

using namespace std;
int P,St,Dr,Mij,Prod,Nr,Rez,Rasp;
int main()
{
    ifstream fin("fact.in");
    ofstream fout("fact.out");

    fin>>P;
    if(P==1)
        fout<<0;
    else
    {
        St=1;
        Dr=50;
        while(St<=Dr)
        {
            Mij=(St+Dr)/2;
            Prod=5;
            Nr=0;
            while(Mij/Prod>0)
            {
                Nr+=Mij/Prod;
                Prod=Prod*5;
            }//while
            if(Nr<P)
                St=Mij+1;
            else
            {
                Dr=Mij-1;
                Rez=Nr;
                Rasp=Mij;
            }//else
        }//while
        if(Rez==P)
            fout<<Rasp;
        else
            fout<<-1;
    }

    fin.close ();
    fout.close();
    return 0;
}