#include <fstream>
using namespace std;
long long  p, st, dr, put, s, aux;
int main ()
{
    ifstream fin ("fact.in");
    ofstream fout ("fact.out");
    fin>>p;
    st=1;
    dr=2000000000;
    while (st<=dr)
    {
        int mid=(st+dr)/2;
        s=0;
        put=5;
        while (mid/put!=0)
        {
            s+=mid/put;
            put*=5;
        }
        if (s>=p)
            dr=mid-1;
        else
            st=mid+1;
    }
    s=0;
    put=5;
    aux=st;
    while (aux/put!=0)
    {
        s+=aux/put;
        put*=5;
    }
    if (s!=p)
        fout<<-1;
    else
        fout<<st;


}