import sequtils,strutils,math,algorithm
var
    N = stdin.readline.parseInt
    S = stdin.readline.split
    A = newSeq[int](0)
if S.len == 1:
    A.add(S[0].parseInt)
    for i in 0..1:
        A.add(stdin.readline.parseInt)
    var
        B = newSeqWith(3, sum(A))
    for i in 0..2:
        B[i] -= A[i]
    B.sort(cmp)
    if B[2] == B[1]:
        B[1] = B[0]
    echo B[1]
else:
    echo "\"assert\""