//#pragma GCC optimize("Ofast")
//#pragma GCC target("avx,avx2,sse,sse2,sse3,ssse3,sse4,abm,popcnt,mmx")
#include <bits/stdc++.h>

using namespace std;

typedef long long ll;
typedef double db;
typedef long double ldb;
typedef complex<double> cd;

constexpr ll INF64 = 9'000'000'000'000'000'000, INF32 = 2'000'000'000, MOD = 1'000'000'007, MAXN = 10'000;
constexpr db PI = acos(-1);
constexpr bool IS_FILE = false, IS_TEST_CASES = false;

random_device rd;
mt19937 rnd32(rd());
mt19937_64 rnd64(rd());

template<typename T>
bool assign_max(T& a, T b) {
	if (b > a) {
		a = b;
		return true;
	}
	return false;
}

template<typename T>
bool assign_min(T& a, T b) {
	if (b < a) {
		a = b;
		return true;
	}
	return false;
}

template<typename T>
T square(T a) {
	return a * a;
}

template<>
struct std::hash<pair<ll, ll>> {
	ll operator() (pair<ll, ll> p) const {
		return ((__int128)p.first * MOD + p.second) % INF64;
	}
};

ll binpow(ll a, ll b) {
	return (b == 0 ? 1 : square(binpow(a, b / 2)) % MOD * (b % 2 ? a : 1) % MOD);
}

ll inv(ll x) {
	return binpow(x, MOD - 2);
}

ll f[MAXN], invf[MAXN], p2[MAXN], invp2[MAXN];

void precalc() {
	f[0] = 1;
	p2[0] = 1;
	invp2[0] = 1;
	ll i2 = inv(2);
	for (ll i = 1; i < MAXN; i++) {
		f[i] = f[i - 1] * i % MOD;
		p2[i] = p2[i - 1] * 2 % MOD;
		invp2[i] = invp2[i - 1] * i2 % MOD;
	}
	invf[MAXN - 1] = inv(f[MAXN - 1]);
	for (ll i = MAXN - 1; i > 0; i--) {
		invf[i - 1] = invf[i] * i % MOD;
	}
}

ll C(ll n, ll k) {
	if (k > n) {
		return 0;
	}
	return f[n] * invf[k] % MOD * invf[n - k] % MOD;
}

void solve() {
	ll n, m;
	cin >> n >> m;
	if (n > m) {
		swap(n, m);
	}
	ll ans = 0;
	for (ll add = m - n; add <= n; add++) {
		ll r1 = n - add, r2 = add;
		ll c1 = m - (add + n - m), c2 = add + n - m;
		ll mul = 1;
		ll now = 0;
		for (ll col = 0; col <= c2; col++) {
			now += C(n, r2) * C(m, c2) % MOD * C(c2, col) % MOD * C(r2, col) % MOD * f[col] % MOD * p2[col] % MOD * f[r1 + r2 * 2 - col * 2] % MOD * mul;
			now += MOD;
			now %= MOD;
			mul *= -1;
		}
		ans += now * invp2[r2] % MOD * invp2[c2] % MOD;
		ans %= MOD;
	}
	cout << ans << '\n';
}

int main() {
	if (IS_FILE) {
		freopen("", "r", stdin);
		freopen("", "w", stdout);
	}
    	ios_base::sync_with_stdio(false);
    	cin.tie(0);
    	cout.tie(0);
	precalc();
	ll t = 1;
	if (IS_TEST_CASES) {
		cin >> t;
	}
	for (ll i = 0; i < t; i++) {
		solve();
	}
}