View Compilation Error

0_0_26763763_1002.cpp: In function 'int main()':
0_0_26763763_1002.cpp:2:71: error: 'fabs' was not declared in this scope
 int main(){double n;while(scanf("%lf",&n)!=EOF)printf("%.2lf\n",fabs(n));return 0;}
                                                                       ^