View Compilation Error

0_0_15406532_29140.cpp: In function 'void solve(std::vector<double>&)':
0_0_15406532_29140.cpp:35:10: error: 'M_PI' was not declared in this scope
   ans *= M_PI;
          ^
0_0_15406532_29140.cpp:81:9: error: 'M_PI' was not declared in this scope
  ans *= M_PI;
         ^