#include <fstream>
using namespace std;
ifstream f ("fact.in");
ofstream g ("fact.out");
long long P, N, nrz, ok, aux, p[]={1,5,25,125,625,3125,15625,78125,390625,1953125,9765625,48828125},k=1;
int main ()
{
    f>>P;
    if (P==0)
        g<<"-1";
    else
    {
        for (N=5; ok==0 && nrz<P; N=N+5)
        {  if(N>=p[k])
        {
            nrz=k+nrz;k++;
        }
           else  nrz++;
        }
        N=N-5;
        if (nrz==P)
            g<<N;
        else
            g<<"-1";
    }
    f.close ();
    g.close ();
    return 0;
}