#include <iostream>
#include <fstream>
using namespace std;
ifstream f("fact.in");
ofstream g("fact.out");
long long p,n,m5,k,cont,cp;
int main()
{
    f>>p;
    if(p==0)
        g<<"1";
    else
    {
        cp=p;
        while(cp%5==0)
            cp=cp/5;
        if(cp==1)
            g<<"-1";
        else
        {
            n=p*5;
            m5=25;
            k=1;
            cont=2;
            while(m5<n)
            {
                while(m5*k<n)
                {
                    n=n-5*(cont-1);
                    k++;
                }
                m5=m5*5;
                cont++;
            }
            g<<n;
        }
    }
    return 0;
}