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#include "bits/stdc++.h" // Tomasz Nowak
using namespace std;     // University of Warsaw
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

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

int add(int a, int b) {
	a += b;
	return a >= mod ? a - mod : a;
}
int mul(int a, int b) {
	return int((a * LL(b)) % mod);
}

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

	int n, m;
	cin >> n >> m;
	
	array<vector<int>, 2> prev, curr;
	for(auto *a : {&prev, &curr})
		for(auto &v : *a)
			v.resize(min(n, m) + 1);
	curr[1][0] = 1;

	FOR(len, 1, n) {
		swap(prev, curr);
		for(auto &v : curr)
			fill(v.begin(), v.end(), 0);

		FOR(good_cnt, 1, min(n, m)) {
			curr[1][good_cnt] = add(
					mul(prev[0][good_cnt], good_cnt),
					mul(prev[1][good_cnt], good_cnt)
			);
			curr[0][good_cnt] = add(
					mul(prev[0][good_cnt], m - good_cnt),
					mul(prev[1][good_cnt - 1], m - good_cnt + 1)
			);
			debug(len, good_cnt, prev[1][good_cnt - 1], m - good_cnt + 1, curr[0][good_cnt]);
		}
		debug(len, curr, prev);
	}

	int answer = 0;
	FOR(good_cnt, 1, min(n, m))
		answer = add(answer, curr[1][good_cnt]);
	cout << answer << '\n';
}