foo.cc:8:4: error: 'MAXN' was not declared in this scope
    8 | }a[MAXN];
      |    ^~~~
foo.cc: In function 'int main()':
foo.cc:19:22: error: 'a' was not declared in this scope
   19 |                 cin>>a[i].pre;
      |                      ^
foo.cc:22:14: error: 'a' was not declared in this scope
   22 |         sort(a+1,a+n+1,cp);
      |              ^
foo.cc:34:36: error: 'cmp' was not declared in this scope; did you mean 'cp'?
   34 |                                 if(cmp(a[j],a[j-1]))
      |                                    ^~~
      |                                    cp
foo.cc:41:36: error: 'cmp' was not declared in this scope; did you mean 'cp'?
   41 |                                 if(cmp(a[j],a[j-1]))
      |                                    ^~~
      |                                    cp

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