View Compilation Error

0_0_33662820_21329.cpp: In function 'int main()':
0_0_33662820_21329.cpp:5:68: error: 'sqrt' was not declared in this scope
     printf("%.2lf\n",sqrt((double)((x1-x2)*(x1-x2)+(y1-y2)*(y1-y2))));
                                                                    ^