MOD = 1_000_000_007
n,m = gets.split.map(&:to_i)

def powmod(v, p)
	return 1 if p == 0
	return v if p == 1
	ret = powmod(v, p / 2)
	ret *= ret
	ret %= MOD
	p % 2 == 1 ? ret * v % MOD : ret
end

ans = 0
sgn = 1
comb = 1
m.downto(1) { |i|
	ans += sgn * powmod(i, n) * comb
	sgn *= -1
	comb *= i * powmod(m + 1 - i, MOD - 2)
	comb %= MOD
}
puts ans % MOD