L = list(map(int, input().split()))
L.sort()
if L[0] == L[1] == L[2]:
    print(L[0])
    exit()
if L[1] == L[2]:
    print(L[0])
    exit()
if L[0] == L[1]:
    print(L[2])
    exit()
for i in range(4):
    if i not in L:
        print(i)
        exit()