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 $*c*_{1}, *c*_{2}, *c*_{3}, *c*_{4}$ and $*c*_{5}$ — the number of coins that the first, second, third, fourth and fifth players respectively have at the end of the game ($0 ≤ *c*_{1}, *c*_{2}, *c*_{3}, *c*_{4}, *c*_{5} ≤ 100$).

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).

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.