
#if 1
#include <iostream>
#include <fstream>
#include <string>
#include <vector>
#include <map>
#include <set>
#include <unordered_map>
#include <unordered_set>
#include <queue>
#include <stack>
#include <array>
#include <deque>
#include <algorithm>
#include <utility>
#include <cstdint>
#include <functional>
#include <iomanip>
#include <numeric>
#include <assert.h>
#include <bitset>
#include <list>
#include <cmath>

auto& in = std::cin;
auto& out = std::cout;
#define all_range(C) std::begin(C), std::end(C)
const double PI = 3.141592653589793238462643383279502884197169399375105820974944;

template<typename Arithmetic, typename Integral>
std::enable_if_t< std::is_unsigned<Integral>::value, Arithmetic>
ipow(Arithmetic bace, Integral n)
{
	//繰り返し二条法
	auto res = (Arithmetic)(1);
	while (n > 0) {
		if (n & 1) res *= bace;
		bace *= bace;
		n >>= 1;
	}
	return res;
}
constexpr bool is_prime(uint32_t N)
{
	if (N <= 1) {
		return false;
	}
	for (size_t i = 2; i * i <= N; ++i)
	{
		if (N % i == 0) {
			return false;
		}
	}
	return true;
}
template <uint64_t MOD> class mint_base;
//mint_base_base型用の累乗関数
template <uint64_t MOD> constexpr mint_base<MOD> m_pow(mint_base<MOD> x, uint64_t n)noexcept;
//mod計算を自動で行う整数テンプレートクラス
template <uint64_t MOD_ = 1000000007>
class mint_base
{
public:
	static constexpr auto MOD = MOD_;
	static_assert(!(MOD <= 2), "MOD cannot be below 2.");
	static_assert(MOD <= (0xFFFFFFFFFFFFFFFF / 2), "MOD is too big");//加算してオーバーフローしない
	static_assert(MOD <= 0xFFFFFFFF, "MOD is too big");//乗算してオーバーフローしない
	constexpr mint_base<MOD> operator+(const mint_base<MOD>& other)const noexcept
	{
		auto v = *this;
		return v += other;
	}
	constexpr mint_base<MOD> operator-(const mint_base<MOD>& other)const noexcept
	{
		auto v = *this;
		return v -= other;
	}
	constexpr mint_base<MOD> operator*(const mint_base<MOD>& other)const noexcept
	{
		auto v = *this;
		return v *= other;
	}
	constexpr auto operator/(const mint_base<MOD>& other)const noexcept
	{
		auto v = *this;
		return v /= other;
	}
	constexpr mint_base<MOD>& operator+=(const mint_base<MOD>& other) noexcept
	{
		a += other.a;
		if (MOD <= a) { a -= MOD; };
		return *this;
	}
	constexpr mint_base<MOD>& operator-=(const mint_base<MOD>& other) noexcept
	{
		if (a >= other.a) {
			a -= other.a;
		}
		else {
			a = (a + MOD) - other.a;
		}
		return *this;
	}
	constexpr mint_base<MOD>& operator*=(const mint_base<MOD>& other) noexcept
	{
#if 1
		a *= other.a;
		a %= MOD;
#else
		//MOD <= (MAXUINT64 / 2)条件下
		uint64_t b = other.a, v = 0;
		while (b > 0) {
			if (b & 1) {
				v += a;
				if (v >= MOD)v -= MOD;
			}
			a += a;
			if (MOD <= a)a -= MOD;
			b >>= 1;
		}
		a = v;
#endif
		return *this;
	}
	constexpr mint_base<MOD>& operator/=(const mint_base<MOD>& other) noexcept
	{
		return *this *= ~other;
	}
	constexpr mint_base<MOD> operator+()const noexcept { return *this; }
	constexpr mint_base<MOD> operator-()const noexcept
	{
		return{ MOD - a, mod_value_tag{} };
	}
	constexpr mint_base<MOD>& operator++() noexcept
	{
		if (MOD <= ++a) { a = 0; };
		return *this;
	}
	constexpr mint_base<MOD>& operator--() noexcept
	{
		if (a <= 0) { a = MOD; };
		--a;
		return *this;
	}
	constexpr mint_base<MOD> operator++(int) noexcept
	{
		auto tmp = *this;
		++* this;
		return tmp;
	}
	constexpr mint_base<MOD> operator--(int) noexcept
	{
		auto tmp = *this;
		--* this;
		return tmp;
	}
	constexpr mint_base<MOD> operator~()const noexcept
	{
		return ipow(*this, e_phi - 1);
	}
	constexpr mint_base<MOD>& operator=(const mint_base<MOD>& other) noexcept
	{
		a = other.a;
		return *this;
	}
	constexpr explicit operator uint64_t()const noexcept
	{
		return a;
	}
	constexpr explicit operator unsigned()const noexcept
	{
		return (unsigned)a;
	}
	static constexpr uint64_t getmod() noexcept
	{
		return MOD;
	}
	constexpr mint_base(uint64_t a_) noexcept :a(a_% MOD) {}
	constexpr mint_base()noexcept : a(0) {}
	struct mod_value_tag {};
	constexpr mint_base(uint64_t a_, mod_value_tag) :a(a_) {}
private:
	static constexpr uint64_t get_e_phi()noexcept {
		//オイラー値の導出
		uint64_t temp = MOD;
		uint64_t m_ = MOD;
		for (uint64_t i = 2; i * i <= m_; ++i)
		{
			if (m_ % i == 0)
			{
				temp = temp / i * (i - 1);
				for (; m_ % i == 0; m_ /= i);
			}
		}
		if (m_ != 1)temp = temp / m_ * (m_ - 1);
		return temp;
	}
	static constexpr uint64_t e_phi = get_e_phi();//オイラー値
	uint64_t a;
};
//mint_base型用の累乗関数
template<uint64_t MOD>constexpr mint_base<MOD> m_pow(mint_base<MOD> x, uint64_t n)noexcept
{
	mint_base<MOD> res = 1;
	while (n > 0)
	{
		if (n & 1)res *= x;
		x *= x;
		n >>= 1;
	}
	return res;
}
//mint_baseの階乗計算
//O(x)時間が必要のため、fact_set関数を推奨する。
template<uint64_t MOD>constexpr mint_base<MOD> fact(mint_base<MOD> x)noexcept
{
	mint_base<MOD> res(1);
	for (uint64_t i = 1; i <= (uint64_t)x; ++i)
	{
		res *= i;
	}
	return res;
}
//mint_baseの階乗計算
//0からxまでの階乗を返す
//O(x)時間が必要
template<uint64_t MOD>std::vector<mint_base<MOD>> fact_set(mint_base<MOD> x = mint_base<MOD>(-1))
{
	mint_base<MOD> res(1);
	std::vector<mint_base<MOD>> set((uint64_t)(x)+1);
	set[0] = 1;
	for (uint64_t i = 1; i <= (uint64_t)x; ++i)
	{
		res *= i;
		set[i] = res;
	}
	return res;
}
//mint_base型のstreamへの出力
template<uint64_t MOD> std::ostream& operator<<(std::ostream& os, mint_base<MOD> i)
{
	os << (uint64_t)i;
	return os;
}
//mint_base型のstreamからの入力
template<uint64_t MOD> std::istream& operator >> (std::istream& is, mint_base<MOD>& i)
{
	uint64_t tmp;
	is >> tmp;
	i = tmp;
	return is;
}
typedef mint_base<> mint;
namespace mint_literal {
	constexpr mint operator""_mi(unsigned long long x)noexcept {
		return mint(x);
	}
}
using namespace mint_literal;
//mint_baseの階乗計算
//0からxまでの階乗を返す
//O(N)
template<int32_t X, uint64_t MOD = mint::MOD>
/*constexpr*/ std::array<mint_base<MOD>, X + 1> fact_set_c()
{
	mint_base<MOD> res(1);
	std::array<mint_base<MOD>, X + 1> set;
	set[0] = 1;
	for (int32_t i = 1; i <= X; ++i)
	{
		res *= i;
		set[i] = res;
	}
	return set;
}

int32_t N,M;
mint pow2[50010];

mint func(int n, int mmax);
mint dp2[5010][5010];
bool used2[5010][5010];
mint func2(int n, int mmax)
{
	if (mmax == 0) {
		return 0_mi;
	}
	auto& memo = dp2[n][mmax];
	if (used2[n][mmax]) {
		return memo;
	}
	used2[n][mmax] = true;

	//memo = func(n-1, mmax, m - 1) + 2_mi*func2(mmax - 1, m - 1);

	//memo = 0;
	//for (size_t i = 0; i <= mmax; i++)
	//{
	//	memo += pow2[mmax - i] * func(n - 1, i);
	//}

	//memo = 0;
	//for (int64_t i = mmax; i >= 1; --i)
	//{
	//	memo += pow2[mmax - i] * func(n - 1, i-1);
	//}
	//return memo;
	return memo = func(n - 1, mmax-1) + 2_mi * func2(n, mmax - 1);
}


mint dp3[5010][5010];
bool used3[5010][5010];
mint func3(int n, int mmax)
{
	if (mmax == 0) {
		return 0_mi;
	}
	auto& memo = dp3[n][mmax];
	if (used3[n][mmax]) {
		return memo;
	}
	used3[n][mmax] = true;

	memo = 0;
	for (size_t i = mmax; i >= 1; --i)
	{
		memo += func(n-1, i) * func2(n, mmax-i);
	}
	return memo;
	//return memo = func(n - 1, mmax) * func2(n, 0) + func3(n, mmax - 1);
}



mint dp[5010][5010];
bool used[5010][5010];
mint func(int n,int mmax)
{
	if (mmax == 1) {
		return pow2[n];
	}
	if (n == 1) {
		return pow2[mmax];
	}
	//if (n == 2) {
	//	return pow2[2* mmax];
	//}

	auto& memo = dp[n][mmax];
	if (used[n][mmax]) {
		return memo;
	}
	used[n][mmax] = true;

	memo = 0;
	return memo = 2_mi * func(n-1,mmax) +
				  2_mi * func(n - 1, 1) * func(n - 1, mmax - 1) +
		func3(n, mmax);
}

int main()
{
    using std::endl;
    in.sync_with_stdio(false);
    out.sync_with_stdio(false);
    in.tie(nullptr);
    out.tie(nullptr);

	pow2[0] = 1;
	for (size_t i = 1; i < 50010; i++)
	{
		pow2[i] = pow2[i - 1] + pow2[i - 1];
	}

    in >> N >> M;
	out << func(N, M) << endl;


    return 0;
}
#endif
