#include <fstream>
using namespace std;
int p;
int zero(int m)
{
	int z = 0, i;
	for (i = 5; i <= m; i = i * 5)z = z + m / i;
	return z;
}
int cautare_binara(int st, int dr)
{
	int mij, zo;
	while (st <= dr)
	{
		mij = (st + dr) / 2;
		zo = zero(mij);
		if (zo == p && st == dr)return mij;
		if (zo == p) dr = mij;
		else if (zo < p)st = mij + 1;
		else dr = mij - 1;
	}
	return -1;
}
int _tmain(int argc, _TCHAR* argv[])
{
	fstream f("fact.in", ios::in);
	fstream g("fact.out", ios::out);
	f >> p;
	g << cautare_binara(1, 999999999);
	f.close();
	g.close();
	return 0;
}