#include <iostream>
#include <fstream>
using namespace std;
ifstream f("fact.in");
ofstream g("fact.out");
long n,p,head,tail,m;
int numar_zero(long long n)
{
    long long p=5,nr=0;
    while(p<=n)
    {
        nr+=(n/p);
        p*=5;
    }
    return nr;
}
void solve()
{
    f>>p; head=1; tail=p*5;
    while(head<=tail)
    {
        m=(head+tail)/2;
        if(numar_zero(m)>=p)tail=m-1;else head=m+1;
    }
    if(numar_zero(head)!=p)g<<-1; else g<<head;
}
int main()
{
    solve();
    return 0;
}