import java.util.*;
import java.io.*;

public class Main {
	public static void main(String[] args) throws Exception {
		new Main().run();
	}

	long pow(long a, long n) {
		long ret = 1;
		for (; n > 0; n >>= 1, a = a * a % MOD) {
			if (n % 2 == 1) {
				ret = ret * a % MOD;
			}
		}
		return ret;
	}

	long inv(long a) {
		return pow(a, MOD - 2);
	}

	final long MOD = (long) 1e9 + 7;

	void run() throws Exception {
		Scanner sc = new Scanner(System.in);
		long N = sc.nextInt();
		long K = sc.nextInt();
		long P = 1;
		for (long i = 0; i < K; ++i) {
			P = P * (N - 1 - i) % MOD;
		}
		long sum = N * (N + 1) % MOD * inv(2) % MOD;
		long ans = P * sum % MOD;

		P = 1;
		for (long i = N - 2; i >= 1; --i) {
			P = P * i % MOD;
		}
		for (long i = K - 2; i >= 1; --i) {
			P = P * inv(i) % MOD;
		}
		for (long i = N - 2 - (K - 2); i >= 1; --i) {
			P = P * inv(i) % MOD;
		}
		for (long i = 1; i <= K; ++i) {
			P = P * i % MOD;
		}
		P = P * inv(2) % MOD;
		sum = (sum - N + MOD) % MOD;
		ans = (ans + P * sum % MOD) % MOD;
		System.out.println(ans);

	}

	void tr(Object... objects) {
		System.out.println(Arrays.deepToString(objects));
	}

}