#include <bits/stdc++.h>
#ifdef __LOCAL__
#include <debug_local.h>
#endif
using namespace std;
template<const int mod, const int modPhi>
struct Mint {
int v;
Mint() { v = 0; }
Mint(int x) { v = x % mod; if (v < 0) v += mod; }
Mint(long long x) { v = x % mod; if (v < 0) v += mod; }
friend bool operator==(const Mint &a, const Mint &b) { return a.v == b.v; }
friend bool operator!=(const Mint &a, const Mint &b) { return a.v != b.v; }
friend bool operator<(const Mint &a, const Mint &b) { return a.v < b.v; }
friend bool operator<=(const Mint &a, const Mint &b) { return a.v <= b.v; }
friend bool operator>(const Mint &a, const Mint &b) { return a.v > b.v; }
friend bool operator>=(const Mint &a, const Mint &b) { return a.v >= b.v; }
Mint& operator+=(const Mint &a) { v += a.v; if (v >= mod) v -= mod; return *this; }
Mint& operator-=(const Mint &a) { v -= a.v; if (v < 0) v += mod; return *this; }
Mint& operator*=(const Mint &a) { v = (1LL * v * a.v) % mod; return *this; }
Mint operator-() { return Mint(-v); }
Mint& operator++() { return *this += 1; }
Mint& operator--() { return *this -= 1; }
friend Mint operator+(Mint a, const Mint b) { return a += b; }
friend Mint operator-(Mint a, const Mint b) { return a -= b; }
friend Mint operator*(Mint a, const Mint b) { return a *= b; }
friend Mint min(Mint a, Mint b) { return (a < b ? b : a); }
friend Mint max(Mint a, Mint b) { return (a > b ? a : b); }
friend Mint power(Mint a, long long b) {
Mint res = 1;
while (b > 0) {
if (b & 1) {
res *= a;
}
a *= a, b >>= 1;
}
return res;
}
friend Mint inv(const Mint &a) { return power(a, modPhi - 1); }
Mint operator/=(const Mint &a) { *this *= inv(a); return *this; }
friend Mint operator/(Mint a, const Mint b) { return a /= b; }
friend istream& operator>>(istream &in, Mint &a) { return in >> a.v; }
friend ostream& operator<<(ostream &out, Mint a) { return out << a.v; }
};
const int mod = 1e9 + 7;
using mint = Mint<mod, mod - 1>;
void testCase() {
int w, h;
cin >> w >> h;
vector<vector<mint>> dp(w + 1, vector<mint> (h + 1, mint(1)));
for (int i = 1; i <= w; i++) {
for (int j = 1; j <= h; j++) {
dp[i][j] = mint(4 * j) * dp[i - 1][j - 1];
dp[i][j] += dp[i - 1][j];
if (j >= 2) dp[i][j] += mint(j * (j - 1) / 2) * dp[i - 1][j - 2];
if (i >= 2) dp[i][j] += mint((i - 1) * j) * dp[i - 2][j - 1];
}
}
cout << dp[w][h] - 1 << endl;
}
int main() {
ios::sync_with_stdio(false);
cin.tie(nullptr);
testCase();
return 0;
}
