#include <iostream>
#include<fstream>
using namespace std;
ifstream f("fact.in");
ofstream g("fact.out");
int factorial (int n)
{if (n==0||n==1)
return 1;
    int i,p=1;
    for (i=1;i<=n;i++)
        p=p*i;
    return p;
}
int nrzero (int n)
{
    int p=0;
    while (n/5)
    {
        p++;
        n=n/5;
    }
    return p;
}
int main ()
{
    int p;
    f>>p;
    if (p==0)
    {
        g<<-1;
        return 0;
    }

int n=5;
while(nrzero(factorial(n))!=p)
n++;
cout<<n;
f.close();
g.close();
}