//Include
#include <fstream>
using namespace std;

//Functii
void bs(int left, int right);
int f(int n);

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

int p;
int n;

//Main
int main()
{
	in >> p;
	if(!p)
	{
		out << 1;
		in.close();
		out.close();
		return 0;
	}
	bs(1, (int)1e9);
	
	n -= n % 5;
	if(!n)
		out << -1;
	else
		out << n;
	
	in.close();
	out.close();
	return 0;
}

void bs(int left, int right)
{
	int mijl = (left + right) / 2;
	int nr0 = f(mijl);
	if(nr0 == p)
		n = mijl;
	else if(left != right)
	{
		if(nr0 > p)
			bs(left, mijl-1);
		else
			bs(mijl+1, right);
	}
}

int f(int n)
{
	int x=0,p=5;
	while(n/p!=0)
	{
		x+=n/p;
		p*=5;
	}
	return x;
}