#include <bits/stdc++.h>
#include <ext/pb_ds/tree_policy.hpp>
#include <ext/pb_ds/assoc_container.hpp>
using namespace std;
using namespace __gnu_pbds;
typedef long long ll;
typedef long double ld;
typedef complex<ld> cd;
typedef pair<int, int> pi;
typedef pair<ll,ll> pl;
typedef pair<ld,ld> pd;
typedef vector<int> vi;
typedef vector<ld> vd;
typedef vector<ll> vl;
typedef vector<pi> vpi;
typedef vector<pl> vpl;
typedef vector<cd> vcd;
template <class T> using Tree = tree<T, null_type, less<T>, rb_tree_tag,tree_order_statistics_node_update>;
#define FOR(i, a, b) for (int i=a; i<(b); i++)
#define F0R(i, a) for (int i=0; i<(a); i++)
#define FORd(i,a,b) for (int i = (b)-1; i >= a; i--)
#define F0Rd(i,a) for (int i = (a)-1; i >= 0; i--)
#define sz(x) (int)(x).size()
#define mp make_pair
#define pb push_back
#define f first
#define s second
#define lb lower_bound
#define ub upper_bound
#define all(x) x.begin(), x.end()
const int MOD = 1000000007;
const ll INF = 1e18;
const int MX = 100001;
int dp[3001][3001];
int ad(int a, int b) { return (a+b)%MOD; }
int mul(int a, int b) { return (ll)a*b%MOD; }
int main() {
ios_base::sync_with_stdio(0); cin.tie(0);
F0R(i,3001) dp[i][0] = dp[0][i] = 1;
FOR(x,1,3001) FOR(y,1,3001) { // rows, cols
if (y > 1) dp[x][y] = ad(dp[x][y],mul(y*(y-1)/2,dp[x-1][y-2]));
if (x > 1) dp[x][y] = ad(dp[x][y],mul((x-1)*y,dp[x-2][y-1]));
dp[x][y] = ad(dp[x][y],mul(4*y,dp[x-1][y-1]));
dp[x][y] = ad(dp[x][y],dp[x-1][y]);
}
int a,b; cin >> a >> b;
cout << (dp[a][b]+MOD-1)%MOD;
}
/* Look for:
* the exact constraints (multiple sets are too slow for n=10^6 :( )
* special cases (n=1?)
* overflow (ll vs int?)
* array bounds
*/
