CF1257F Make Them Similar

Let's call two numbers similar if their binary representations contain the same number of digits equal to $ 1 $ . For example: - $ 2 $ and $ 4 $ are similar (binary representations are $ 10 $ and $ 100 $ ); - $ 1337 $ and $ 4213 $ are similar (binary representations are $ 10100111001 $ and $ 1000001110101 $ ); - $ 3 $ and $ 2 $ are not similar (binary representations are $ 11 $ and $ 10 $ ); - $ 42 $ and $ 13 $ are similar (binary representations are $ 101010 $ and $ 1101 $ ). You are given an array of $ n $ integers $ a_1 $ , $ a_2 $ , ..., $ a_n $ . You may choose a non-negative integer $ x $ , and then get another array of $ n $ integers $ b_1 $ , $ b_2 $ , ..., $ b_n $ , where $ b_i = a_i \oplus x $ ( $ \oplus $ denotes bitwise XOR). Is it possible to obtain an array $ b $ where all numbers are similar to each other?

The first line contains one integer $ n $ ( $ 2 \le n \le 100 $ ). The second line contains $ n $ integers $ a_1 $ , $ a_2 $ , ..., $ a_n $ ( $ 0 \le a_i \le 2^{30} - 1 $ ).

If it is impossible to choose $ x $ so that all elements in the resulting array are similar to each other, print one integer $ -1 $ . Otherwise, print any non-negative integer not exceeding $ 2^{30} - 1 $ that can be used as $ x $ so that all elements in the resulting array are similar.