import scala.io.StdIn

object Solution {
  def main(args: Array[String]): Unit = {
    val n = StdIn.readInt()
    val m = StdIn.readLine().split(" ").map(_.toInt)
    val scores = (n - 1 to 0 by -1).foldLeft(Vector.fill(n)(IndexedSeq.empty[Int])) { (s, i) =>
      val v = (1 to limit(m, i) - i).map { j =>
        if (i + j == n) 1
        else {
          val max = j min s(i + j).length
          val t = (0 until max).foldLeft((0, 1)) { (state, k) =>
            val a = mult(state._2, j - k)
            (sum(state._1, mult(s(i + j)(k), a)), a)
          }
          t._1
        }
      }
      s.updated(i, v)
    }
    println(scores(0).foldLeft(0) { (total, score) => sum(total, score) })
  }

  def limit(m: IndexedSeq[Int], i: Int): Int = {
    if (i == m.size - 1 || m(i + 1) < m(i)) i + 1
    else limit(m, i + 1)
  }

  def mult(a: Int, b: Int): Int = (a.toLong * b % 1000000007).toInt

  def sum(a: Int, b: Int): Int = (a + b) % 1000000007
}