View Compilation Error

0_0_25727508_8885.cpp: In function 'int main()':
0_0_25727508_8885.cpp:19:60: error: 'rd1' was not declared in this scope
             sum=sum-acos((R*R+L*L-r*r)/(2*R*L))*2*R+(2*pai-rd1-acos((r*r+R*R-L*L)/(2*r*R))*2)*r;
                                                            ^