#include <fstream>

using namespace std;

int main()
{
    ifstream f("fact.in");
    ofstream g("fact.out");
   int p,n,t,a,x;
    f>>p;
    a=1;
    n=0;
    t=5;
    while(p>t)
        {
        a=a+1;
        x=a;
        while(x-1>0)
            {t=5*t;
            x=x-1;
            }
        t=t+a-1;
        }
    if(p==t)
        n=-1;
    if(n!=-1)
        n=5*(p-a+1);
    g<<n;
    return 0;
}