#include <bits/stdc++.h> #define file(name) if (fopen(name".inp", "r")) { freopen(name".inp", "r", stdin); freopen(name".out", "w", stdout); } using namespace std; #define int long long const int N = 3005; const int MOD = 1e9 + 7; int h, w; int dp[N][N]; int32_t main() { ios_base::sync_with_stdio(false); cin.tie(0), cout.tie(0); // file("A") else file("task"); cin >> h >> w; for(int i = 0; i <= w; i++) dp[0][i] = 1; for(int i = 1; i <= h; i++) { dp[i][0] = 1; for(int j = 1; j <= w; j++) { dp[i][j] = dp[i - 1][j] + 4 * j * dp[i - 1][j - 1]; if(i >= 2) dp[i][j] += dp[i - 2][j - 1] * j * (i - 1); if(j >= 2) dp[i][j] += dp[i - 1][j - 2] * j * (j - 1) / 2; dp[i][j] %= MOD; } } cout << (dp[h][w] - 1 + MOD) % MOD; return 0; }