#include<bits/stdc++.h>
#define ll long long int
#define pb push_back
#define mp make_pair
#define FOR(i,n) for(i=0;i<(n);++i)
#define FORe(i,n) for(i=1;i<=(n);++i)
#define FORr(i,a,b) for(i=(a);i<(b);++i)
#define FORrev(i,n) for(i=(n);i>=0;--i)
#define F0R(i,n) for(int i=0;i<(n);++i)
#define F0Re(i,n) for(int i=1;i<=(n);++i)
#define F0Rr(i,a,b) for(ll i=(a);i<(b);++i)
#define F0Rrev(i,n) for(int i=(n);i>=0;--i)
#define ii pair<ll,ll>
#define vi vector<ll>
#define vii vector<ii>
#define ff first
#define ss second
#define cd complex<double>
#define vcd vector<cd>
#define ldd long double
#define dbgLine cout<<"Line : "<<__LINE__<<'\n'
#define all(x) (x).begin(),(x).end()
using namespace std;
const short int __PRECISION = 10;
const ll MOD = 1e9+7;
const ll INF = 1e17 + 1101;
const ll LOGN = 17;
const ll MAXN = 3001;
const ll ROOTN = 320;
const ldd PI = acos(-1);
const ldd EPS = 1e-7;
ll dp[MAXN][MAXN];
#define C(a) ((a*a-a)/2)
ll DP(int i, int j)
{
if(i < 0 or j < 0) return 0;
ll& t = dp[i][j];
if(t != -1) return t;
t = 0;
t += DP(i-1,j);
t += 4*j*DP(i-1,j-1);
t += (i-1)*j*DP(i-2,j-1);
t += C(j)*DP(i-1,j-2);
t %= MOD;
//assert(t == dp[i][j]);
return t;
}
int main()
{
ios_base::sync_with_stdio(false);
cin.tie(NULL);
cout.tie(NULL);
int i, j;
FOR(i, MAXN)
FOR(j, MAXN)
dp[i][j] = (i == 0 || j == 0) ? 1 : -1;
cin>>i>>j;
cout<<(DP(i, j) + MOD - 1) % MOD << endl;
return 0;
}
