Initial Bet

time limit per test

memory limit per test

input

output

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.

Input

The input consists of a single line containing five integers c1,?c2,?c3,?c4 and c5 ? the number of coins that the first, second, third, fourth and fifth players respectively have at the end of the game (0?≤?c1,?c2,?c3,?c4,?c5?≤?100).

Output

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).

Sample test(s)

input

2 5 4 0 4

output

input

4 5 9 2 1

output

-1

Note

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.

解题思路：水题，不解释，8分钟交题，虽然一激动少了个条件，忘记判非零了，但是还是在10分钟内出了这题，创了我的cf最快出题纪录了～～～

AC代码：

#include #include #include #include #include #include #include #include