import sys
import numpy as np
read = sys.stdin.buffer.read
readline = sys.stdin.buffer.readline
readlines = sys.stdin.buffer.readlines

n=int(input())
p=list(map(int, input().split()))

k=np.prod(np.array(p, dtype='int64'))

while not len(str(k))==1:
    k=sum(list(map(int, str(k))))
    
print(k)