#!/usr/bin/env python

#-*- coding: utf-8 -*-



from collections import defaultdict

from math import factorial as f

from fractions import gcd as g



l = [int (i) for i in input ().split ()]

d = defaultdict (int)

for i in l: d [i] += 1

print([i for i in d if d [i] == 1][0])



#!/usr/bin/env python

#-*- coding: utf-8 -*-



A, B, C = [int (i) for i in input ().split ()]

print(A ^ B ^ C)
#!/usr/bin/env python
# -*- coding: utf-8 -*-
from collections import defaultdict
from math import factorial as f
from fractions import gcd as g

l = [int(i) for i in input().split()]
d = defaultdict(int)
for i in l:
    d[i] += 1
print([i for i in d if d[i] == 1][0])

#!/usr/bin/env python
# -*- coding: utf-8 -*-
A, B, C = [int(i) for i in input().split()]
print(A ^ B ^ C)

-from collections import defaultdict -from math import factorial as f -from fractions import gcd as g - -l = [int(i) for i in input().split()] -d = defaultdict(int) -for i in l: -    d[i] += 1 -print([i for i in d if d[i] == 1][0]) +A, B, C = [int(i) for i in input().split()] +print(A ^ B ^ C)