A goat in a kitchen garden

http://acm.timus.ru/problem.aspx?space=1&num=1084

Time Limit: 2.0 second

Memory Limit: 1 000 K

Someone has let a goat in a square kitchen-garden and had bound it to a stake. The stake is driven into the ground in the very midst of the square. The goat is hungry as a hunter and very voracious, and eats everything that can be reached without leaving the square and tearing the roap. What area of the kitchen-garden will be ate round?

1. Input

contains lengths of the garden sides and a cord length in meters (natural numbers not exceeding 100, located in one line and separated with a space).

2. Output

should contain an area of the kitchen-garden (in square meters to within 3 symbols after a decimal point), ate round by the goat.

3. Sample Input

{{{10 6 }}}

4. Sample Output

{{{95.091 }}}

   1 /*Written by czk*/
   2 #include <iostream>
   3 #include <iomanip>
   4 #include <cmath>
   5 using namespace std;
   6 
   7 int main()
   8 {
   9   int n, r;
  10   cin >> n >> r;
  11   if(n >= 2*r) {
  12     cout << fixed <<showpoint << setprecision(3) << 3.14159266*r*r << endl;
  13   } else if(n < r *1.41421356237){
  14     cout << fixed <<showpoint << setprecision(3) << 1.0*n*n << endl;
  15   } else {
  16     double theta = acos(n/2.0/r);
  17     cout << fixed << showpoint <<setprecision(3) << sin(theta)*r*n*2+r*r*(3.14159266-theta*4) << endl;
  18   }
  19 }