import scala.collection.mutable.*
import scala.io.StdIn.*
import scala.util.chaining.*
import scala.math.*
import scala.reflect.ClassTag
import scala.util.*
import scala.annotation.tailrec
import scala.collection.mutable



object ModInt:
  opaque type ModInt = Long
  inline def zero: ModInt = 0
  inline def one: ModInt = 1
  extension (value: Long)
    inline def toModInt(using inline mod: Int): ModInt =  value % mod
    inline def unsafeAsModInt: ModInt = value
  extension (value: Int)
    inline def toModInt(using inline mod: Int): ModInt = value % mod
    inline def unsafeAsModInt: ModInt = value
  trait Converter[T]:
    inline def convert(value: T)(using inline mod: Int): ModInt
  inline given Converter[Int] with
    override inline def convert(value: Int)(using inline mod: Int) = value.toModInt
  inline given Converter[Long] with
    override inline def convert(value: Long)(using inline mod: Int) = value.toModInt
  inline given Converter[ModInt] with
    override inline def convert(value: ModInt)(using inline mod: Int) = value
  extension (modInt: ModInt)
    inline def toLong(using inline mod: Int): Long = (modInt + mod) % mod
    inline def rawValue: Long = modInt
    inline def inverse(using inline mod: Int): ModInt =
      var x = modInt
      var y = mod.toLong
      var a = 1L
      var b = 0L
      var c = 0L
      var d = 1L
      while y != 0 do
        val q = x / y
        val e = a - c * q
        val f = b - d * q
        a = c
        b = d
        c = e
        d = f
        x = y
        y = c * modInt + d * mod
      require(x.abs == 1L)
      if x == 1 then a % mod else -a % mod
    inline def powMod(exp: Long)(using inline mod: Int): ModInt =
      var result = 1L
      var base = modInt
      var e = exp
      while e > 0 do
        if (e & 1) == 1 then
          result = result * base % mod
        base = base * base % mod
        e >>= 1
      result
    inline def powMod(exp: Int)(using inline mod: Int): ModInt = powMod(exp.toLong)
  extension [L: Converter, R: Converter] (left: L)
    inline def +(right: R)(using inline mod: Int): ModInt = (summon[Converter[L]].convert(left) + summon[Converter[R]].convert(right)).toModInt
    inline def -(right: R)(using inline mod: Int): ModInt = (summon[Converter[L]].convert(left) - summon[Converter[R]].convert(right)).toModInt
    inline def *(right: R)(using inline mod: Int): ModInt = (summon[Converter[L]].convert(left) * summon[Converter[R]].convert(right)).toModInt
    inline def /(right: R)(using inline mod: Int): ModInt = (summon[Converter[L]].convert(left) * summon[Converter[R]].convert(right).inverse).toModInt



import ModInt.*
inline given mod: Int = 1000000007

class Bit(size: Int):
  private val vec = Array.fill(size){zero}
  inline def get(position: Int)(using inline mod: Int): ModInt =
    var pos = position
    var result = zero
    while pos >= 0 do
      result += vec(pos)
      pos -= ~pos & (pos + 1)
    result
  inline def add(position: Int, value: ModInt)(using inline mod: Int) =
    var pos = position
    while pos < size do
      vec(pos) += value
      pos += ~pos & (pos + 1)
  inline def getAll(using inline mod: Int): ModInt = get(size - 1)

@main def main =
  val n = readLine.toInt
  val length = readLine.split(' ').map(_.toInt)
  val str = readLine
  val prev = Array.fill(n + 1){-1}
  val lastPosition = Array.fill(26){0}
  for (c, i) <- str.zipWithIndex do
    prev(i + 1) = lastPosition(c - 'a')
    lastPosition(c - 'a') = i + 1
  val useAll = Array.fill(n + 1){zero}.tap(_(0) = one)
  val allPattern = Bit(n + 1).tap(_.add(0, one))
  for i <- 1 to n do
    val len = length(i - 1)
    val p = prev(i)
    val unique = allPattern.get(i) - allPattern.get(p)
    val expand = useAll(p)
    val newPattern = (unique + expand) * len
    useAll(i) = unique + expand
    allPattern.add(i, newPattern)
  println((allPattern.getAll - 1).toLong)