Ages

Source: beecrowd

Version: Phuoc Hung OJ Extended

Problem Statement

Read a sequence of integer ages ending at the first negative integer. The negative sentinel is not an age. Compute the arithmetic mean of all preceding nonnegative ages and print exactly two digits after the decimal point. At least one age is guaranteed.

Input

Each line contains one integer age or the negative terminating value.

Output

Print the mean age with exactly two digits after the decimal point.

Subtasks

• Subtask 1 (20%): Exactly one age in [1,100] before sentinel -1.
• Subtask 2 (30%): 1 to 10 ages in [0,100]; the sentinel is in [-1000,-1].
• Subtask 3 (50%): 1 to 1000 ages in [0,120]; the sentinel is in [-1000,-1].

Examples

Example 1

Input

34
56
44
23
-1

Output

39.25

Explanation

The four ages sum to 157; dividing by four gives 39.25. The negative sentinel is excluded.

Example 2

Input

0
20
-1

Output

10.00

Explanation

Age zero is valid, so the mean of 0 and 20 is 10.00.