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Problem K
Trials and Triangulations

More math? You got it. That’s what computers do, they compute.

Heron’s formula gives the area, $A$, of a triangle with sides $a$, $b$, and $c$ as $A = \sqrt{s(s-a)(s-b)(s-c)}$ where $s = (a+b+c)/2$.

Write a program that prompts for three integers, $a$, $b$, and $c$, denoting the lengths of the sides of a triangle. Calculate the area, and print the result.

Hint: You can use the sqrt function in the math module.

Input

Input consists of three lines. The first line consists of one integer $a$. The second line consists of one integer $b$. The third line consists of one integer $c$. It is guaranteed that $1 \leq a, b, c \leq 100$ and that the values can form a triangle.

Output

Output one line with one floating point number $A$, the area of the triangle. The output number should have an absolute or relative error of at most $10^{-9}$.

Sample Input 1 Sample Output 1
1
1
1
0.433012701892219
Sample Input 2 Sample Output 2
1
2
3
0.000000000000000
Sample Input 3 Sample Output 3
2
2
3
1.984313483298443
Sample Input 4 Sample Output 4
12
9
19
41.952353926806062
Sample Input 5 Sample Output 5
5
4
3
6.000000000000000
Sample Input 6 Sample Output 6
5
12
13
30.000000000000000

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