CF204B Little Elephant and Cards

The Little Elephant loves to play with color cards. He has $ n $ cards, each has exactly two colors (the color of the front side and the color of the back side). Initially, all the cards lay on the table with the front side up. In one move the Little Elephant can turn any card to the other side. The Little Elephant thinks that a set of cards on the table is funny if at least half of the cards have the same color (for each card the color of the upper side is considered). Help the Little Elephant to find the minimum number of moves needed to make the set of $ n $ cards funny.

The first line contains a single integer $ n $ $ (1

On a single line print a single integer — the sought minimum number of moves. If it is impossible to make the set funny, print -1.

In the first sample there initially are three cards lying with colors 4, 4, 7. Since two of the three cards are of the same color 4, you do not need to change anything, so the answer is 0. In the second sample, you can turn the first and the fourth cards. After that three of the five cards will be of color 7.