N = int(input())
P = list(map(int,input().split()))
t = 1
f = 0
for e in P:
    if e > 0:
        t *= e%9
    else:
        f = 1
        break

if f == 1:
    print(0)
elif t == 0:
    print(9)
else:
    while t >= 10:
        t = sum(map(int, str(t)))
    print(t)