import operator
def lonely(a):
return reduce(operator.__xor__,a)
n=input()
a=map(int,raw_input().split())
print lonely(a)
aW1wb3J0IG9wZXJhdG9yCmRlZiBsb25lbHkoYSk6CiAgcmV0dXJuIHJlZHVjZShvcGVyYXRvci5fX3hvcl9fLGEpCgpuPWlucHV0KCkKYT1tYXAoaW50LHJhd19pbnB1dCgpLnNwbGl0KCkpCnByaW50IGxvbmVseShhKQ==