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#include <bits/stdc++.h>
using namespace std;
using LL = long long;
#define FOR(i, l, r) for(int i = (l); i <= (r); ++i)
#define REP(i, n) FOR(i, 0, (n) - 1)
#define ssize(x) int(x.size())
template<class A, class B> auto& operator<<(ostream &o, pair<A, B> p) {
    return o << '(' << p.first << ", " << p.second << ')';
}
template<class T> auto operator<<(ostream &o, T x) -> decltype(x.end(), o) {
    o << '{'; int i = 0; for(auto e : x) o << (", ")+2*!i++ << e; return o << '}';
}
#ifdef DEBUG
#define debug(x...) cerr << "[" #x "]: ", [](auto... $) {((cerr << $ << "; "), ...); }(x), cerr << '\n'
#else
#define debug(...) {}
#endif

template<int mod>
struct modular {
	int val;
	modular() { val = 0; }
	modular(const LL& v) {
		val = int((-mod <= v && v <= mod) ? (int) v : v % mod);
		if(val < 0) val += mod;
	}
	int to_int() { return val; }

	friend ostream& operator<<(ostream &os, const modular &a) {
		return os << a.val;
	}
	friend istream& operator>>(istream &is, modular &a) {
		return is >> a.val;
	}

	friend bool operator==(const modular &a, const modular &b) {
		return a.val == b.val;
	}
	friend bool operator!=(const modular &a, const modular &b) {
		return !(a == b);
	}
	friend bool operator<(const modular &a, const modular &b) {
		return a.val < b.val;
	}
	friend bool operator<=(const modular &a, const modular &b) {
		return a.val <= b.val;
	}

	modular operator-() const { return modular(-val); }
	modular& operator+=(const modular &m) {
		if((val += m.val) >= mod) val -= mod;
		return *this;
	}
	modular& operator-=(const modular &m) {
		if((val -= m.val) < 0) val += mod;
		return *this;
	}
	modular& operator*=(const modular &m) {
		val = (LL) val * m.val % mod;
		return *this;
	}
	friend modular qpow(modular a, LL n) {
		if(n == 0) return 1;
		if(n % 2 == 1) return qpow(a, n - 1) * a;
		return qpow(a * a, n / 2);
	}
	friend modular inv(const modular &a) {
		assert(a != 0); return qpow(a, mod - 2);
	}
	modular& operator/=(const modular &m) { 
		return (*this) *= inv(m); 
	}
	modular operator++(int) {
		modular res = (*this);
		(*this) += 1;
		return res;
	}

	friend modular operator+(modular a, const modular &b) { return a += b; }
	friend modular operator-(modular a, const modular &b) { return a -= b; }
	friend modular operator*(modular a, const modular &b) { return a *= b; }
	friend modular operator/(modular a, const modular &b) { return a /= b; }
};
using mint = modular<int(1e9 + 7)>;
// using mint = modular<998244353>;

int main() {
    cin.tie(0)->sync_with_stdio(0);

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

    vector dp(n + 1, vector(n + 1, array<mint, 2>{0, 0}));
    dp[0][0][1] = 1;
    REP(i, n) {
        FOR(j, 1, n) {
            dp[i + 1][j][0] = dp[i][j - 1][1] * (m - j + 1)
                            + dp[i][j][0] * (m - j);

            dp[i + 1][j][1] = (dp[i][j][0] + dp[i][j][1]) * j;
        }
    }

    mint ans = 0;
    FOR(j, 1, n)
        ans += dp[n][j][1];
    cout << ans << "\n";
}