#include <fstream>

using namespace std;

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

int n,p,i;
int MAX = 100000000;

int zero(int x)
{
	int suma = 0;
	while (x)
	{
		suma += x/5;
		n /= 5;
	}
	return suma;
}

int caut_binar(int st, int p, int dr)
{
	int m, k = -1;
	int x;
	while (st <= dr)
	{
		m = (st+dr) / 2;
		if (zero(m) == x) k = m;
		if (zero(m) > x) dr = m - 1;
		if (zero(m) < x) st = m + 1;
	}
	return k;
}

int main ()
{
	f >> p;
	n = caut_binar(1,p,MAX);
	g << n;
	f.close();
	g.close();
	return 0;
}