aaa = list(map(str,input().split()))
abc = set(aaa)
line = ['0','1','2','3']

if len(abc) == 1:
    print(aaa[0])
elif len(abc) == 3:
    for i in line:
        if i not in abc:
            print(i)
else:
    for j in abc:
        if aaa.count(j) == 1:
            print(j)