import sys
read = sys.stdin.buffer.read
readline = sys.stdin.buffer.readline
readlines = sys.stdin.buffer.readlines
sys.setrecursionlimit(10 ** 7)

import numpy as np

n = int(readline())
k = np.array(list(map(int, read().split())), dtype=np.int64).prod()
k = str(sum(map(int, str(k))))
while len(k) != 1:
    k = str(sum(map(int, k)))
print(k)