def d(num):
    total = 0
    for digit in str(num):
        total += int(digit)
    return total
    
    
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)