View Compilation Error

0_0_13952230_8388.cpp: In function 'void init()':
0_0_13952230_8388.cpp:26:54: error: 'M_PI' was not declared in this scope
  scanf("%d%d%d%lf", &n, &m, &bgn, &ini), ini = 2.0 * M_PI * ini / 360.0;
                                                      ^
0_0_13952230_8388.cpp: In function 'double angle(Point, Point)':
0_0_13952230_8388.cpp:39:9: error: 'M_PI' was not declared in this scope
  return M_PI - ret;
         ^
0_0_13952230_8388.cpp: In function 'void work()':
0_0_13952230_8388.cpp:48:23: error: 'M_PI' was not declared in this scope
   double best = 5.0 * M_PI;
                       ^