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#define _USE_MATH_DEFINES
#include <bits/stdc++.h>
#ifdef LOC
#include "debuglib.h"
#else
#define deb(...)
#define DBP(...)
#endif
using namespace std;
using   ll         = long long;
using   Vi         = vector<int>;
using   Pii        = pair<int, int>;
#define pb           push_back
#define mp           make_pair
#define x            first
#define y            second
#define rep(i, b, e) for (int i = (b); i < (e); i++)
#define each(a, x)   for (auto& a : (x))
#define all(x)       (x).begin(), (x).end()
#define sz(x)        int((x).size())

constexpr int MOD = int(1e9)+7;

ll modPow(ll a, ll e, ll m) {
	ll t = 1 % m;
	while (e) {
		if (e % 2) t = t*a % m;
		e /= 2; a = a*a % m;
	}
	return t;
}

struct Zp {
	ll x;
	Zp() : x(0) {}
	Zp(ll a) : x(a%MOD) { if (x < 0) x += MOD; }
	#define OP(c,d) Zp& operator c##=(Zp r) { x = x d; return *this; } Zp operator c(Zp r) const { Zp t = *this; return t c##= r; }
	OP(+, +r.x - MOD*(x+r.x >= MOD));
	OP(-, -r.x + MOD*(x-r.x < 0));
	OP(*, *r.x % MOD);
	OP(/, *r.inv().x % MOD);
	Zp operator-() const { return Zp(0)-*this; }
	Zp inv() const { return pow(MOD-2); }
	Zp pow(ll e) const{ return modPow(x,e,MOD); }
	void print() { cerr << x; }
};

int main() {
	cin.sync_with_stdio(0); cin.tie(0);
	cout << fixed << setprecision(12);

	int n, m;
	cin >> n >> m;

	vector<Zp> f1(n+1), f2(n+1);
	vector<Zp> g1(n+1), g2(n+1);
	f1[0] = 1;

	rep(i, 0, n) {
		rep(j, 0, sz(f2)) {
			f2[j] = (f1[j] + g1[j]) * j;
			g2[j] = g1[j] * (m-j);
			if (j > 0) g2[j] += f1[j-1] * (m-j+1);
		}
		swap(f1, f2);
		swap(g1, g2);
	}

	Zp ans = accumulate(all(f1), Zp());
	cout << ans.x << '\n';
	return 0;
}