CF478A.Initial Bet
普及/提高-
通过率：0%
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题目描述
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.
输入格式
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.
输出格式
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).
输入输出样例
输入#1
2 5 4 0 4
输出#1
3
输入#2
4 5 9 2 1
输出#2
-1
说明/提示
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.