#include <iostream>
#include <fstream>
using namespace std;
int main()
{
    ifstream in("fact.in");
    ofstream out("fact.out");
    long p,t,i=1,k2=0,k5=0,m=0;
    in>>p;
    while(m<p)
    {
        t=i;
        while(t%2==0)
        {
            k2++;t/=2;
        }
        while(t%5==0)
        {
            k5++;t/=5;
        }

    m=k5;
    if(k2<k5) m=k2;
    i++;
    }
    if(m==p) out<<i-1;
        else
             out<<-1;
    return 0;
}