#include <bits/stdc++.h>
#pragma GCC optimize ("O2,unroll-loops")
//#pragma GCC optimize("no-stack-protector,fast-math")
//#pragma GCC target("sse,sse2,sse3,ssse3,sse4,popcnt,abm,mmx,avx,tune=native")

using namespace std;
typedef long long ll;
typedef long double ld;
typedef pair<int, int> pii;
typedef pair<pii, int> piii;
typedef pair<ll, ll> pll;
#define debug(x) cerr<<#x<<'='<<(x)<<endl;
#define debugp(x) cerr<<#x<<"= {"<<(x.first)<<", "<<(x.second)<<"}"<<endl;
#define debug2(x, y) cerr<<"{"<<#x<<", "<<#y<<"} = {"<<(x)<<", "<<(y)<<"}"<<endl;
#define debugv(v) {cerr<<#v<<" : ";for (auto x:v) cerr<<x<<' ';cerr<<endl;}
#define all(x) x.begin(), x.end()
#define pb push_back
#define kill(x) return cout<<x<<'\n', 0;

const int inf=1000000010;
const ll INF=10000000000000010LL;
const int mod=1000000007;
const int N=5010;

ll n, m, k, u, v, x, y, t, a, b, ans;
ll dp[N][N];

int main(){
	ios_base::sync_with_stdio(false);cin.tie(0);cout.tie(0);
	//freopen("input.txt", "r", stdin);
	//freopen("output.txt", "w", stdout);
	dp[1][1]=2;
	for (int m=2; m<N; m++) dp[1][m]=dp[1][m-1]*2%mod;
	for (int n=2; n<N; n++){
		dp[n][1]=dp[n-1][1]*2%mod;
		for (int m=2; m<N; m++){
			ll sum=(dp[n][m-1]-dp[n-1][m-1]*m)*2%mod;
			dp[n][m]=(dp[n-1][m]*(m+1) + dp[n-1][m-1]*(m-1) + sum)%mod;
		}
	}
	cin>>n>>m;
	if (dp[n][m]<0) dp[n][m]+=mod;
	cout<<dp[n][m]<<"\n";
	
	return 0;
}