#include <iostream>
#include <fstream>

using namespace std;

int n;
ifstream f("cifra.in");
ofstream g("cifra.out");

int putere(int m,int j,int x)
{
	if (j)
		putere((m*x) % 10, j - 1, x);
	else
		return m;
}

int main()
{
	int s;
	f >> n;
	while (!f.eof()) {
		f >> n;
		s = 0;
		for (int i = 1; i <= n; i++)
		{
			s += putere(i % 10, i - 1, i % 10);

		}
		g << s % 10 << "\n";
	}
	f.close();
	g.close();
	return 0;
}