# 入力例2の言葉はいけない
# 難しいのは最初の掛け算だけ、あとは簡単
# 解き方が思いつかないので実験してみた
# かける数字同士の各桁をかけた和を使えばいいか

N = int(input())
P = list(map(int, input().split()))
product = P[0]

for i in range(1, N):
    list1 = []
    for p1 in str(product):
        list1.append(int(p1))
    list2 = []
    for p2 in str(P[i]):
        list2.append(int(p2))
    product = 0
    for p1 in list1:
        for p2 in list2:
            product += p1*p2
#print(product)

while True:
    temp = 0
    for s in str(product):
        temp += int(s)
    #print(temp)
    if len(str(temp)) == 1:
        break
    else:
        product = temp
    
print(temp)