// IOI 2021
#include <bits/stdc++.h>
using namespace std;

#define endl '\n'
#define ends ' '
#define die(x) return cout << x << endl, 0
#define all(v) v.begin(), v.end()
#define sz(x) (int)(x.size())
void debug_out() { cerr << endl; }
template <typename Head, typename... Tail>
void debug_out(Head H, Tail... T) { cerr << ends << H; debug_out(T...); }
#define debug(...) cerr << "{" << #__VA_ARGS__ << "}:", debug_out(__VA_ARGS__)
typedef long long ll;
typedef pair<int, int> pii;
const int INF = 1e9;
const ll MOD = 1e9 + 7;
 
////////////////////////////////////////////////////////////////////
 
const int N = 5e3 + 5;

int DP[N][N], S[N][N];

int main() {
 
	ios::sync_with_stdio(0), cin.tie(0), cout.tie(0);
	mt19937 Rnd(time(0));
	
	// DP[i][j] = (j + 1) * DP[i - 1][j] + S[i][j];
	// S[i][j] = Sigma(k = 1, k < j, k * F[i - 1][j] * 2 ^ (j - k - 1));
	// S[i][j] = S[i][j - 1] * 2 + (j - 1) * DP[i - 1][j - 1]; 

	for (int i = 1; i < N; i++) DP[0][i] = DP[i][0] = 1;
	for (int i = 1; i < N; i++) {
		for (int j = 1; j < N; j++) {
			S[i][j] = (2LL * S[i][j - 1] % MOD + 1LL * (j - 1) * DP[i - 1][j - 1] % MOD) % MOD;
			DP[i][j] = (1LL * (j + 1) * DP[i - 1][j] % MOD + S[i][j]) % MOD;
		}
	}
	
	int n, m; cin >> n >> m;
	cout << DP[n][m] << endl;

	return 0;
}
