#include <bits/stdc++.h> using namespace std; void setup() { ios_base::sync_with_stdio(0); cin.tie(0); cout.tie(0); } const long long mod = 1e9 + 7; int n, m; long long f[5001][5001]; int main() { setup(); cin >> n >> m; f[0][0] = 1; for (int i = 0; i <= n; ++i) { for (int j = 0; j <= m; ++j) { if (i == 0 || j == 0) { f[i][j] = 1; continue; } (f[i][j] = f[i][j - 1] + f[i - 1][j - 1] * i * 4) %= mod; if (2 <= j) { (f[i][j] += f[i - 1][j - 2] * i * (j - 1)) %= mod; } if (2 <= i) { (f[i][j] += f[i - 2][j - 1] * i * (i - 1) / 2) %= mod; } } } cout << (f[n][m] - 1 + mod) % mod; return 0; }