View Compilation Error

0_0_39497216_15813.cpp: In function 'void solve()':
0_0_39497216_15813.cpp:53:20: error: 'abs' was not declared in this scope
   53 |                 if(abs(t-pre.t)<abs(x-pre.x)) bad=1;
      |                    ^~~
0_0_39497216_15813.cpp:59:20: error: 'abs' was not declared in this scope
   59 |                 if(abs(nxt.t-t)<abs(nxt.x-x)) bad=1;
      |                    ^~~