#include <bits/stdc++.h>
#define AOTSUKI

using namespace std;
constexpr bool isMultiCase = 0;

// #include "angel/math/modint.hpp"

using ll = long long;
template <class T> constexpr int len(const T &c) {
    return int(std::ssize(c));
}
template <class T> using V = vector<T>;
template <class T> using RevPq = priority_queue<T, vector<T>, greater<T>>;
constexpr char eoln = '\n';
#define L(i, l, r) for (int i = (l); i < (r); ++i)
#define R(i, l, r) for (int i = (r) - 1; i >= (l); --i)
#define ALL(x) (x).begin(), (x).end()
#define fi first
#define se second

constexpr ll mod = 1000000007;

constexpr int MaxN = 5000;
ll comb[MaxN + 1][MaxN + 1];
ll fact[MaxN + 1];
ll pw2[MaxN + 1], ipw2[MaxN + 1];
constexpr ll i2 = 500000004;

void init() {
    L(i, 0, MaxN + 1) L(j, 0, MaxN + 1) comb[i][j] = 0;
    comb[0][0] = 1;
    L(i, 1, MaxN + 1) {
        comb[i][0] = 1;
        L(j, 1, i + 1) {
            comb[i][j] = comb[i - 1][j] + comb[i - 1][j - 1];
            comb[i][j] %= mod;
        }
    }
    fact[0] = pw2[0] = ipw2[0] = 1;
    L(i, 1, MaxN + 1) {
        fact[i] = fact[i - 1] * i % mod;
        pw2[i] = pw2[i - 1] * 2 % mod;
        ipw2[i] = ipw2[i - 1] * i2 % mod;
    }
}

void solve() {
    int n, m; cin >> n >> m;
    ll ans = 0;

    L(a, 0, n + 1) {
        // a : degree 2
        int b = n + a - m;
        if (b < 0 or b > m) continue;

        ll sc = 0;
        L(p, 0, min(a, b) + 1) {
            ll sign = p & 1 ? mod - 1 : 1;
            ll val = comb[a][p] * comb[b][p] % mod * fact[p] % mod * pw2[p] % mod;
            val *= fact[n + a - 2 * p]; val %= mod;
            sc += sign * val; sc %= mod;
        }
        sc *= comb[n][a] % mod * comb[m][b] % mod * ipw2[a + b] % mod; sc %= mod;
        ans += sc;
    }
    ans %= mod;
    cout << ans << endl;
}

int main() {
    ios::sync_with_stdio(false);
    cin.tie(nullptr);
    cout.tie(nullptr);

    init();
    if (not isMultiCase) {
        solve();
    } else {
        int t;
        cin >> t;
        while (t--) solve();
    }
}