// Created by PhantomCracker. Copyright(c) PhantomCracker

#include <iostream>
#include <fstream>
#include <cmath>
#include <limits>
using namespace std;

int verificare(int nr)
{
	int count = 0;
	int putere_cinci = 5;
	while(nr/putere_cinci > 0)
	{
		count = count + nr/putere_cinci;
		putere_cinci = putere_cinci * 5;
	}
}

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

	int stanga, dreapta, mijloc;
	int p;
	f>>p;

	stanga = 1;
	dreapta = p*5;
	while(stanga <= dreapta)
	{
		mijloc = (stanga + dreapta)/2;
		if(verificare(mijloc) < p) stanga = mijloc + 1;
		else dreapta = mijloc - 1;
	}
	if(verificare(stanga) == p) g<<stanga;
	else g<<-1;

	cout<<endl;
	return 0;
}