#include <fstream>
using namespace std;

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

int main()
{
    int p, n, k=0, i=0, m;
    f>>p;
    n=p*4;
    m=n;
    while (k!=p && k<p)
    {
        i++;
        k=0;
        while (m!=0)
        {
            m=m/5;
            k=k+m;
        }
        m=n+i;
    }
    if (k!=p)
        g<<-1;
    else
        if (p==0)
            g<<1;
        else
            g<<m-1;
return 0;
f.close();
g.close();
}