n = int(input())
p = list(map(int, input().split()))

while len(p) > 1:
    if len(p) % 2 == 1:
        p.append(1)

    q = list()
    for i in range(0,len(p),2):
        q.append(p[i+0]*p[i+1])

    p = q

ans = p[0]
while ans >= 10:
    s = str(ans)
    ans = 0
    for c in s:
        ans += ord(c) - ord('0')

print(ans)