A9575. Initial Bet

There are five people playing a game called "Generosity". Each person gives some non-zero number of coins $b$ as an initial bet. After all players make their bets of $b$ coins, the following operation is repeated for several times: a coin is passed from one player to some other player.

Your task is to write a program that can, given the number of coins each player has at the end of the game, determine the size $b$ of the initial bet or find out that such outcome of the game cannot be obtained for any positive number of coins $b$ in the initial bet.

There are five people playing a game called "Generosity". Each person gives some non-zero number of coins $b$ as an initial bet. After all players make their bets of $b$ coins, the following operation is repeated for several times: a coin is passed from one player to some other player.

Your task is to write a program that can, given the number of coins each player has at the end of the game, determine the size $b$ of the initial bet or find out that such outcome of the game cannot be obtained for any positive number of coins $b$ in the initial bet.

Print the only line containing a single positive integer $b$ — the number of coins in the initial bet of each player. If there is no such value of $b$ , then print the only value "-1" (quotes for clarity).

In the first sample the following sequence of operations is possible:

1. One coin is passed from the fourth player to the second player;
2. One coin is passed from the fourth player to the fifth player;
3. One coin is passed from the first player to the third player;
4. One coin is passed from the fourth player to the second player.