#include <iostream>
#include <fstream>
#include <cmath>
using namespace std;

ifstream f("fact.in");
ofstream g("fact.out");

unsigned zero(unsigned n)
{
    unsigned nr=0;
    while(n%10==0)
    {
        nr++;
        n/=10;
    }
    return nr;
}

int main()
{
    long p;
    unsigned n=1,i;
    f>>p;
    if(floor(p)!=p)
        g<<-1;
    else
    {
        for(i=1;;i++)
        {
            n*=i;
            if(zero(n)==p)
            {
                g<<i; break;
            }
        }
    }
    g.close();
    f.close();
    return 0;
}