View Compilation Error

0_0_21369110_25622.cpp: In function 'int main()':
0_0_21369110_25622.cpp:15:23: error: 'abs' was not declared in this scope
   puts(k1 >= abs(x - y) and (k1 <= n - x or k2 + n >= x + y) ? "Not lying" : "Lying");
                       ^