View Compilation Error

0_0_17084723_22144.cpp: In function 'int main()':
0_0_17084723_22144.cpp:15:55: error: 'sqrt' was not declared in this scope
 z=sqrt((x[i]-x[j])*(x[i]-x[j])+(y[i]-y[j])*(y[i]-y[j]));
                                                       ^