#include <stdio.h>

int main()
{
	int num;
	int box;

	scanf("%d", &num);

	box = (num % 10);
	box = box + (num / 10);
	for(int i = 0; i < 100; i++)
	{
		box = (box % 10) + (box / 10);
		if((0 <= box) && (box <= 9))
		{
			printf("%d\n", box);
			return 0;
		}
	}
}