#include <fstream>

using namespace std;
ifstream f("fact.in");
ofstream g("fact.out");
unsigned long long p, sol, st, dr, mij, nr;
unsigned long long fact5(unsigned long long x)
{
	unsigned long long p = 5, sol = 0;
	while (p <= x)
	{
		sol += x / p;
		p *= 5;
	}
	return sol;
}
int main()
{
	f >> p;
	st = 1;
	dr = static_cast<unsigned long long>(1) << 62;
	while (st <= dr)
	{
		mij = (st + dr) / 2;
		nr = fact5(mij);
		if (nr >= p)
		{
			sol = mij;
			dr = mij - 1;
		}
		else
			st = mij + 1;
	}
	g << sol;
	return 0;
}