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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...$){((cerr<<$<<"; "),...)<<'\n';}(x)
#else
#define debug(...) {}
#endif

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

	constexpr LL mod = 1'000'000'007;
	auto mno = [&](LL a, LL b) {
		return a * b % mod;
	};
	auto pot = [&](LL a, LL b) {
		LL z = 1;
		while (b) {
			if (b % 2) {
				z = mno(z, a);
			}
			a = mno(a, a);
			b /= 2;
		}
		return z;
	};
	int n, m;
	cin >> n >> m;
	const LL odwm = pot(m, mod - 2);
	debug(n, m);
	vector<vector<LL>> dp(n + 1, vector<LL>(n + 2));
	vector<vector<LL>> dp2(n + 1, vector<LL>(n + 2));
	dp[1][1] = m;
	const int ogr = min(n, m);
	FOR(i, 1, n - 1) {
		FOR(j, 0, ogr) {
			dp2[i + 1][j] += (dp2[i][j] + dp[i][j]) * j;
			dp2[i + 1][j] %= mod;
			dp[i + 1][j] += dp[i][j] * (m - j);
			dp[i + 1][j] %= mod;
			dp[i + 1][j + 1] += dp2[i][j] * (m - j);
			dp[i + 1][j + 1] %= mod;
		}
	}
	debug(dp);
	debug(dp2);
	LL ans = 0;
	FOR(i, 0, n) {
		ans += dp2[n][i];
	}
	ans %= mod;
	cout << ans << '\n';
}