Domino

Description:

Input:

The first line contains integer n (1 ≤ n ≤ 100), denoting the number of dominoes Valera has. Next n lines contain two space-separated integers x_i, y_i (1 ≤ x_i, y_i ≤ 6). Number x_i is initially written on the upper half of the i-th domino, y_i is initially written on the lower half.

Output:

Print a single number — the minimum required number of seconds. If Valera can't do the task in any time, print  - 1.

Sample Input:

2
4 2
6 4

Sample Output:

0

Sample Input:

1
2 3

Sample Output:

-1

Sample Input:

3
1 4
2 3
4 4

Sample Output:

1

Note:

In the first test case the sum of the numbers on the upper halves equals 10 and the sum of the numbers on the lower halves equals 6. Both numbers are even, so Valera doesn't required to do anything.

In the second sample Valera has only one piece of domino. It is written 3 on the one of its halves, therefore one of the sums will always be odd.

In the third case Valera can rotate the first piece, and after that the sum on the upper halves will be equal to 10, and the sum on the lower halves will be equal to 8.