foo.cpp: In function 'void solve()':
foo.cpp:17:20: error: 'abs' was not declared in this scope
      cout<<(abs(y-x)/(m-n))<<endl;
                    ^
foo.cpp:19:22: error: 'abs' was not declared in this scope
      cout<<(l-abs(y-x))/(n-m)<<endl; 
                      ^