N = int(input())
P = list(map(int, input().split()))

K = 1
for p in P:
    K *= p
    if K == 0:
        print(K)
        exit()

age = list(map(int, str(K)))
while len(age) > 1:
    age[0:2] = list(map(int, str(sum(age[0:2]))))
print(age[0])