#include <iostream>
#include <cmath>
#include <fstream>
#include <iomanip>

using namespace std;
long long int zerouri(unsigned long long int nr)
{
	int cnt = 0;
	while (nr)
	{
		cnt+= nr / 5;
		nr /= 5;
	}
	return cnt;
}
int main()

{
	ifstream fin("fact.in");
	ofstream fout("fact.out");
		
	unsigned long long int Numar_zerouri,stocat=-1,var,variabila_de_zerouri,last_stocat;
	fin >> Numar_zerouri;
	Numar_zerouri = Numar_zerouri * 5;
	for (int i = Numar_zerouri; i > 0; i-=5)
	{
		var = i;
		variabila_de_zerouri=zerouri(var);

		if (variabila_de_zerouri == Numar_zerouri/5)
		{
			stocat = var;
		}

		if (Numar_zerouri / 5 > variabila_de_zerouri)
			break;

	}
	if (Numar_zerouri == 0)
		fout << 1;
	else 
	fout << stocat;

	system("pause>nul");
}