#include <cstdlib>

#include <vector>

using namespace std;

class EllysNumberGuessing {

public:

	int getNumber(vector <int> guesses, vector <int> answers) {

		const int LIMIT = 1000000000;

		int N = guesses.size();

		int res = -2; // not find

		vector<int> options{ guesses[0] + answers[0], guesses[0] - answers[0]};

		for (int i = 0; i < options.size(); i++) {

			int x = options[i];

			bool valid = (x >= 1 && x <= LIMIT);

			for (int j = 1; j < N; j++) {

				valid = valid && (abs(guesses[j] - x) == answers[j]);

			}

			if (valid) {

				if (res == -2) {

					res = x;

				} else {

					res = -1;

				}

			}

		}

		return res;

	}

};