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.

The input consists of a single line containing five integers *c*_{1}, *c*_{2}, *c*_{3}, *c*_{4} and *c*_{5} — the number of coins that the first, second, third, fourth and fifth players respectively have at the end of the game (0 ≤ *c*_{1}, *c*_{2}, *c*_{3}, *c*_{4}, *c*_{5} ≤ 100).

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:

- One coin is passed from the fourth player to the second player;
- One coin is passed from the fourth player to the fifth player;
- One coin is passed from the first player to the third player;
- One coin is passed from the fourth player to the second player.

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