#include <fstream>

using namespace std;

int main()
{
    ifstream fin("fact.in");
    ofstream fout("fact.out");

    int n=0,aux,aux2,p,p2,nr2,nr5,s=0,P;
    fin>>P;
    if(P==0)
    fout<<1;
    else
    {
    while(s<P)
    {
    aux=n;
    aux2=n;
    p=2;
    nr2=0;
    while(aux>0)
    {
        aux=aux/p;
        nr2=nr2+n/p;
        p=p*2;
    }
    nr5=0;
    p2=5;
    while(aux2>0)
    {
        aux2=aux2/p2;
        nr5=nr5+n/p2;
        p2=p2*5;
    }
    if(nr2<nr5)
    s=nr2;
    else
    s=nr5;
    if(s==P)
    fout<<n;
    else
    n++;
    }
    if(s>P)
    fout<<-1;
    }


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