initial_input = input()
num = initial_input.split(" ")
ans = 0
for i in range(8):
    if int(num[i + 1]) - int(num[i]) == 2:
        ans = int(num[i]) + 1
        break
            
if ans == 0:
    if num[0] == "2":
        ans = 1
    else:
        ans = 10
print(ans)