Language: C++

using namespace std;
#include<bits/stdc++.h>
#define BEGIN ios_base::sync_with_stdio(0);cin.tie(0)
#define END return EXIT_SUCCESS
#define FOR(I,A,B) for((I)=(A);(I)<(B);(I)++)
#define REP(I,N) FOR(I,0,N)
#define UP(I,A,B) for((I)=(A);(I)<=(B);(I)++)
#define DW(I,A,B) for((I)=(A);(I)>=(B);(I)--)
#define IN(P) cin>>(P)
#define IN2(P1,P2) cin>>(P1)>>(P2)
#define IN3(P1,P2,P3) cin>>(P1)>>(P2)>>(P3)
#define INS(I,N,V) REP(I,N) cin>>V[I]
#define INS2(I,N,V1,V2) REP(I,N) cin>>V1[I]>>V2[I];
#define INS3(I,N,V1,V2,V3) REP(I,N) cin>>V1[I]>>V2[I]>>V3[I];
#define OUT(P) cout<<P<<endl
#define OUT2(P1,P2) cout<<P1<<" "<<P2<<endl
#define OUT3(P1,P2,P3) cout<<P1<<" "<<P2<<" "<<P3<<endl
#define OUTS(I,N,V) REP(I,N) cout<<V[i]<<endl
#define ALL(C) (C).begin(),(C).end()
#define RALL(C) (C).rbegin(),(C).rend()
#define mp make_pair
#define pb push_back
typedef unsigned long ul;
typedef unsigned int ui;
template<class T> inline bool chmax(T& a, T b) { if (a < b) { a = b; return true; } return false; }
template<class T> inline bool chmin(T& a, T b) { if (a > b) { a = b; return true; } return false; }
long H,W;

inline void solve(){
  IN2(H,W);
  UP(h,2,H){
    a=h*W;
    hh=(H-h)/2;
    b=hh*W;
    c=(H-h-hh)*W;
    chmin(ans,max(a,max(b,c))-min(a,min(b,c)));
    ww=W/2;
    b=(H-h)*WW;
    c=(H-h)*(W-ww);
    chmin(ans,max(a,max(b,c))-min(a,min(b,c)));
  }
  UP(w,2,W){
    a=H*w;
    ww=(W-w)/2;
    b=H*ww;
    c=H*(W-w-ww);
    chmin(ans,max(a,max(b,c))-min(a,min(b,c)));
    hh=H/2;
    b=hh*(W-w);
    c=(H-hh)*(W-w);
    chmin(ans,max(a,max(b,c))-min(a,min(b,c)));
  }
  OUT(ans);
}

int main(int argc,char**argv){
  BEGIN;
  solve();
  END;
}


Compiler output:
a.cc: In function 'void solve()':
a.cc:31:6: error: 'h' was not declared in this scope
   31 |   UP(h,2,H){
      |      ^
a.cc:7:24: note: in definition of macro 'UP'
    7 | #define UP(I,A,B) for((I)=(A);(I)<=(B);(I)++)
      |                        ^
a.cc:32:5: error: 'a' was not declared in this scope
   32 |     a=h*W;
      |     ^
a.cc:33:5: error: 'hh' was not declared in this scope
   33 |     hh=(H-h)/2;
      |     ^~
a.cc:34:5: error: 'b' was not declared in this scope
   34 |     b=hh*W;
      |     ^
a.cc:35:5: error: 'c' was not declared in this scope
   35 |     c=(H-h-hh)*W;
      |     ^
a.cc:36:11: error: 'ans' was not declared in this scope; did you mean 'abs'?
   36 |     chmin(ans,max(a,max(b,c))-min(a,min(b,c)));
      |           ^~~
      |           abs
a.cc:37:5: error: 'ww' was not declared in this scope
   37 |     ww=W/2;
      |     ^~
a.cc:38:13: error: 'WW' was not declared in this scope; did you mean 'W'?
   38 |     b=(H-h)*WW;
      |             ^~
      |             W
a.cc:42:6: error: 'w' was not declared in this scope
   42 |   UP(w,2,W){
      |      ^
a.cc:7:24: note: in definition of macro 'UP'
    7 | #define UP(I,A,B) for((I)=(A);(I)<=(B);(I)++)
      |                        ^
a.cc:43:5: error: 'a' was not declared in this scope
   43 |     a=H*w;
      |     ^
a.cc:44:5: error: 'ww' was not declared in this scope
   44 |     ww=(W-w)/2;
      |     ^~
a.cc:45:5: error: 'b' was not declared in this scope
   45 |     b=H*ww;
      |     ^
a.cc:46:5: error: 'c' was not declared in this scope
   46 |     c=H*(W-w-ww);
      |     ^
a.cc:47:11: error: 'ans' was not declared in this scope; did you mean 'abs'?
   47 |     chmin(ans,max(a,max(b,c))-min(a,min(b,c)));
      |           ^~~
      |           abs
a.cc:48:5: error: 'hh' was not declared in this scope
   48 |     hh=H/2;
      |     ^~
a.cc:53:7: error: 'ans' was not declared in this scope; did you mean 'abs'?
   53 |   OUT(ans);
      |       ^~~
a.cc:15:22: note: in definition of macro 'OUT'
   15 | #define OUT(P) cout<<P<<endl
      |                      ^