import scala.annotation.tailrec

object Main {
  val MOD = BigInt(1000000007)

  def main(args: Array[String]): Unit = {
    val sc = new java.util.Scanner(System.in)
    val total = sc.nextInt()
    val a = sc.nextInt()
    val b = sc.nextInt()

    val c_total_a = (permutation(total, a) / permutation(a, 1))
    val c_total_b = (permutation(total, b) / permutation(b, 1))
    val excepts = c_total_a + c_total_b

    val ans_total = BigInt(2).<<(total) - excepts - 1
    val ans = ans_total % MOD

    println(ans)
  }

  @tailrec
  def permutation(n: Int, k: Int, memo: BigInt = 1): BigInt = {
    if (n == k) {
      memo
    } else {
      permutation(n - 1, k, memo * n)
    }
  }
}
