def d(n):
    ans = 0
    while n > 0:
        ans += n % 10
        n //= 10
    return ans
    
    
n = int(input())
s = input().split()
x = []
for i in s:
    x.append(int(i))
ans = 1
for i in x:
    ans *= i
while ans>9:
    ans = d(ans)
print(ans)