s=list(map(int,input().split()))
t=list(set(s))
if len(t)==1:
    print(s[0])
    exit()
if len(t)==2:
    for x in t:
        if s.count(x)==1:
            print(x)
            exit()
if len(t)==3:
    if 1 not in t:
        print(1)
        exit()
    if 2 not in t:
        print(2)
        exit()
    if 3 not in t:
        print(3)
        exit()
    if 0 not in t:
        print(0)
        exit()