// yuki 933 おまわりさんこいつです
// 2019.11.30 bal4u

#include <stdio.h>
#include <ctype.h>
#include <string.h>

int getchar_unlocked(void);
#define gc() getchar_unlocked()

int in() {   // 非負整数の入力
	int n = 0; int c;
	do c = gc();
	while (isspace(c));
	do n = 10 * n + (c & 0xf); while ((c = gc()) >= '0');
	return n;
}

void ins(char *s) {
	int c;
	while (isspace(c = gc()));
	do *s++ = c;
	while ((c = gc()) >= '0');
	*s = 0;
}

int s2c(char *s) {
	int a = 0;
	while (*s) a += *s++ & 0xf;
	return a;
}

int i2c(int n) {
	int a = 0;
	while (n) a += n % 10, n /= 10;
	return a;
}

int main()
{
	int i, N, t, ans;
	char P[30];
	
	ans = 1;
	N = in();
	while (N--) {
		ins(P);
		t = s2c(P);
		if (t == 0) { puts("0"); return 0; }
		ans = i2c(ans * t);
	}
	while (ans >= 10) ans = i2c(ans);
	putchar(ans+'0'), putchar('\n');
	return 0;
}