417. Heavy Disc
Time limit per test: 0.5 second(s)
Memory limit: 262144 kilobytes
input: standard
output: standard



Consider a heavy disc on the plane, centered at (x0,y0) with radius r, with the origin strictly outside it. The density of the disc is given by formula

p(x,y) = ln(x^2+y^2)

What is the mass of the disc?

Input
The input file contains three integer numbers x0, y0, r (-100 ≤ x0, y0 ≤ 100, 1 ≤ r ≤ 100).

Output
Output one real number — the mass of the disc. Your answer will be considered correct if it is within 10-12 relative error of the exact answer.

Example(s)
sample input
sample output
3 4 2
40.449586576894895
