#include <iostream>
#include <fstream>
#include <time.h>

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%10;
}

int main()
{
// clock_t tStart = clock();
	int s,x,j;
	f >> n;
	while (!f.eof()) {
		f >> n;
		s = 0;
		for (int i = 1; i <= n; i++)
		{
			x = 1;
			for (j = 1; j <= i && x==1; j++)
			{
				if (putere(i % 10, j, i % 10) == i % 10)
				{
					x = 0;
			//		cout << j;
				}
			}
			s += putere(i % 10, (i - 1), i % 10);

		}
		g << s % 10 << "\n";
	}
	f.close();
	g.close();
//	printf("Time taken: %.2fs\n", (double)(clock() - tStart) / CLOCKS_PER_SEC);
	return 0;
}