#include <iostream> #include <vector> using namespace std; using ll = long long; const ll mod = 1000000007; const int maxn = 3000 + 1; ll dp[maxn][maxn]; bool ready[maxn][maxn]; ll sum(ll x) { return ((x * (x-1)) / 2) % mod; } ll solve(ll h, ll w) { if (h < 0 || w < 0) return 0; if (h == 0 || w == 0) return 1; if (ready[h][w]) return dp[h][w]; ll ans = 0; // place nothing ans = solve(h-1, w); // place 1 ans += (solve(h-1, w-1) * w * 4) % mod; ans %= mod; // place 2 in same row ans += (solve(h-1, w-2) * sum(w)) % mod; ans %= mod; // place 2 in same column ans += (solve(h-2, w-1) * (h-1) * w) % mod; ans %= mod; ready[h][w] = true; dp[h][w] = ans; return ans; } int main() { int h, w; cin >> h >> w; cout << (solve(h, w) - 1 + mod) % mod << '\n'; }