Initial Bet

1000ms

262144K

Description:

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 Input:

2 5 4 0 4

Sample Output:

Sample Input:

4 5 9 2 1

Sample Output:

-1

Note:

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.

Informação

Provedor Codeforces

Código CF478A