#include <iostream>
#include <fstream>

using namespace std;

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

int p,imp,contor,aux,poz;
int verificare (int x)
{
    imp=5;
    contor=0;
    while (x/imp>0)
    {
        contor+=x/imp;
        imp*=5;
    }
    return contor;
}
int main()
{
    in>>p;
    poz=0;
    for (int i=1<<30;i>0;i=i>>1)
    {
        if (verificare(poz+i)<=p)
            poz+=i;
    }
    if (poz==4)
        out<<1;
    if (p%2==1)
        out<<-1;
    else
        out<<poz-4;
    return 0;
}