Enter a sequence of ~N~ integers ~A_1, A_2, \ldots, A_N~.

Print the average of the negative elements to the screen.

Input

• The first line contains an integer ~N~.
• The next line contains ~N~ integer numbers ~A_1, A_2, \ldots, A_N~.

Output

• Print the average of the negative elements, rounded to two decimal places. If there are no negative numbers in the sequence, print ~-1~.

Sample Input

5
-1 2 -3 4 -5 

Sample Output

-3.00

Constraints

• ~1 \leq N \leq 10^5~.
• ~|A_i| \leq 10^9~.