n = int(input())
a = list(map(int, input().split()))
k = 1
for i in range(n): k *= a[i]

def keta(x):
    ret = 0
    while(x):
        ret += x % 10
        x = x // 10
    return ret

ans = keta(k)
while(ans > 10): ans = keta(ans)
print(ans)