import sys

line = [int(i) for i in input().split()]
if line[0] != 1:
    print("1")
    sys.exit()

if line[8] != 10:
    print("10")
    sys.exit()

for i in range(9):
    if line[i+1] != line[i] + 1:
        print(line[i] + 1)
        sys.exit()