import java.util.Scanner;

public class Main {
	public static void main(String[] args) {
		solver();
	}

	final static long MOD = 1_000_000_007;
	static long[] fact;

	static void solver() {
		Scanner sc = new Scanner(System.in);
		long n = sc.nextLong();
		int m = sc.nextInt();
		long[] dp = new long[m + 1];
		fact = new long[m + 1];
		fact[0] = 1;
		fact[1] = 1;
		dp[1] = 1;
		for (int i = 2; i <= m; i++) {
			fact[i] = fact[i - 1] * (i % MOD) % MOD;
		}
		for (int i = 2; i <= m; i++) {
			dp[i] = pow(i, n);
			for (int j = 1; j < i; j++) {
				dp[i] -= nCk(i, j) * dp[j] % MOD;
				if (dp[i] < 0)
					dp[i] += MOD;
				dp[i] %= MOD;
			}
		}
		System.out.println(dp[m]);
	}

	static long inv(long a, long mod) {
		a = a % mod;
		long b = mod;
		long p = 1, q = 0;
		while (b > 1) {
			long c = b / a;
			b = b % a;
			q = q - p * c;
			long d = b;
			b = a;
			a = d;
			d = p;
			p = q;
			q = d;
		}
		while (q < 0)
			q += mod;
		return q;
	}

	static long nCk(int n, int k) {
		if (n < k)
			return 0;
		else {
			return (fact[n] * inv(fact[n - k], MOD) % MOD * inv(fact[k], MOD)) % MOD;
		}
	}

	static long pow(long a, long n) {
		long A = a;
		long ans = 1;
		while (n >= 1) {
			if (n % 2 == 0) {
				A = (A * A) % MOD;
				n /= 2;
			} else if (n % 2 == 1) {
				ans = ans * A % MOD;
				n--;
			}
		}
		return ans;
	}

}