View Compilation Error

0_0_31525514_22978.cpp: In function 'int main()':
0_0_31525514_22978.cpp:7:67: error: 'sqrt' was not declared in this scope
             printf("%.2f\n",R=sqrt((X1-X2)*(X1-X2)+(Y1-Y2)*(Y1-Y2)));
                                                                   ^