チャレンジ失敗をした。

## solution

$3$分割する場合はちょうどやり、$2$分割を$2$回する場合は最初の分割を総当たりし次は真ん中で。

+----+-----+-----+
|    |     |     |
|    |     |     |
|    |     |     |
|    |     |     |
|    |     |     |
+----+-----+-----+

+----+-----------+
|    |           |
|    |           |
|    +-----------+
|    |           |
|    |           |
+----+-----------+


## implementation

#include <cstdio>
#include <algorithm>
#include <cassert>
#define repeat(i,n) for (int i = 0; (i) < int(n); ++(i))
#define repeat_from(i,m,n) for (int i = (m); (i) < int(n); ++(i))
using ll = long long;
using namespace std;
template <class T> inline void setmin(T & a, T const & b) { a = min(a, b); }

constexpr ll inf = ll(1e18)+9;
int main() {
// input
ll h, w; scanf("%lld%lld", &h, &w);
auto maxdiff = [&](ll ah, ll aw, ll bh, ll bw, ll ch, ll cw) {
assert (0 <= ah and ah <= h);
assert (0 <= bh and bh <= h);
assert (0 <= ch and ch <= h);
assert (0 <= aw and aw <= w);
assert (0 <= bw and bw <= w);
assert (0 <= cw and cw <= w);
ll as = ah * aw;
ll bs = bh * bw;
ll cs = ch * cw;
assert (as + bs + cs == h * w);
return max(abs(as - bs), max(abs(bs - cs), abs(cs - as)));
};
// solve
ll result = inf;
{ // // hr, hr
ll ah = h / 3;
ll bh = (h - ah) / 2;
ll ch = h - ah - bh;
setmin(result, maxdiff(ah, w, bh, w, ch, w));
}
{ // // vr, vr
ll aw = w / 3;
ll bw = (w - aw) / 2;
ll cw = w - aw - bw;
setmin(result, maxdiff(h, aw, h, bw, h, cw));
}
{ // // vr, hr
ll ah = h;
repeat_from (aw,0,w+1) {
ll bw = w - aw;
ll cw = w - aw;
ll bh = h / 2;
ll ch = h - bh;
setmin(result, maxdiff(ah, aw, bh, bw, ch, cw));
}
}
{ // // hr, vr
ll aw = w;
repeat_from (ah,0,h+1) {
ll bh = h - ah;
ll ch = h - ah;
ll bw = w / 2;
ll cw = w - bw;
setmin(result, maxdiff(ah, aw, bh, bw, ch, cw));
}
}
// output
printf("%lld\n", result);
return 0;
}