View Compilation Error

0_0_24806981_31524.cpp: In function 'int calc(int)':
0_0_24806981_31524.cpp:57:89: error: 'M_PI' was not declared in this scope
   if(sgn(det(vec(seg[i]),poi(-1,0)))!=0&&sgn(abs(calcang(seg[i][0])-calcang(seg[i][1]))-M_PI)>0)flag=0;
                                                                                         ^
0_0_24806981_31524.cpp:60:22: error: 'M_PI' was not declared in this scope
    e[++tot]=(event){-M_PI,i,0};
                      ^