Language: C++

#include <stdio.h>
#include <iostream>
#include <algorithm>
using namespace std;
int main(void){
    long long H, W;
    cin >> H >> W;

    if(H % 3 == 0 || W % 3 == 0){
        cout << 0 << endl;
    } else {
        long long mini = LLONG_MAX;
        for(long long i=1; i<H; i++){
            long long a = i * W;
            long long b = (H-i)*(W/2);
            long long c = H * W - a - b;
            if(max({a, b, c}) - min({a, b, c}) < mini){
                mini = max({a, b, c}) - min({a, b, c});
            }

            long long a = i * W;
            long long b = (H-i)/2*W;
            long long c = H * W - a - b;
            if(max({a, b, c}) - min({a, b, c}) < mini){
                mini = max({a, b, c}) - min({a, b, c});
            }
            
        }

        for(long long i=1; i<W; i++){
            long long a = i * H;
            long long b = (W-i)*(H/2);
            long long c = H * W - a - b;
            if(max({a, b, c}) - min({a, b, c}) < mini){
                mini = max({a, b, c}) - min({a, b, c});
            }

            long long a = i * H;
            long long b = (W-i)/2*H;
            long long c = H * W - a - b;
            if(max({a, b, c}) - min({a, b, c}) < mini){
                mini = max({a, b, c}) - min({a, b, c});
            }
        }
        
        cout << mini << endl;
    }
    return 0;
}


Compiler output:
a.cc: In function 'int main()':
a.cc:12:26: error: 'LLONG_MAX' was not declared in this scope
   12 |         long long mini = LLONG_MAX;
      |                          ^~~~~~~~~
a.cc:4:1: note: 'LLONG_MAX' is defined in header '<climits>'; this is probably fixable by adding '#include <climits>'
    3 | #include <algorithm>
  +++ |+#include <climits>
    4 | using namespace std;
a.cc:21:23: error: redeclaration of 'long long int a'
   21 |             long long a = i * W;
      |                       ^
a.cc:14:23: note: 'long long int a' previously declared here
   14 |             long long a = i * W;
      |                       ^
a.cc:22:23: error: redeclaration of 'long long int b'
   22 |             long long b = (H-i)/2*W;
      |                       ^
a.cc:15:23: note: 'long long int b' previously declared here
   15 |             long long b = (H-i)*(W/2);
      |                       ^
a.cc:23:23: error: redeclaration of 'long long int c'
   23 |             long long c = H * W - a - b;
      |                       ^
a.cc:16:23: note: 'long long int c' previously declared here
   16 |             long long c = H * W - a - b;
      |                       ^
a.cc:38:23: error: redeclaration of 'long long int a'
   38 |             long long a = i * H;
      |                       ^
a.cc:31:23: note: 'long long int a' previously declared here
   31 |             long long a = i * H;
      |                       ^
a.cc:39:23: error: redeclaration of 'long long int b'
   39 |             long long b = (W-i)/2*H;
      |                       ^
a.cc:32:23: note: 'long long int b' previously declared here
   32 |             long long b = (W-i)*(H/2);
      |                       ^
a.cc:40:23: error: redeclaration of 'long long int c'
   40 |             long long c = H * W - a - b;
      |                       ^
a.cc:33:23: note: 'long long int c' previously declared here
   33 |             long long c = H * W - a - b;
      |                       ^