import java.io._
import java.util.StringTokenizer
import scala.util.control.Breaks.{breakable,break}
import scala.collection.mutable.{Map, Stack, Queue, PriorityQueue, Set}

object Main extends App {
  val in = new InputReader(System.in)
  val pw = new PrintWriter(System.out)

  val s = in.next()
  val t = in.next()

  val sl = s.length
  val tl = t.length

  //
  val indices = Array.fill[List[Int]](26)(Nil)
  for (i <- 0 until sl) {
    val ind = s(i).toInt - 97
    indices(ind) = i :: indices(ind)
  }

  val hoge: Array[(Array[Int], Int)] = // (indices, length)
    indices.map{ indice =>
      (indice.reverse.toArray, indice.length)
    }


  def check(i: Int, nowi: Int, cnum: Int): Boolean = {
    hoge(cnum)._1(i) > nowi
  }

  // 条件を満たす最小の値を返す
  def binarySearch(min: Int, max: Int, nowi: Int, cnum: Int): Int = {
    val mid: Int = (max + min) / 2
      (max - min) match{
      case 0 | 1 =>
        check(min, nowi, cnum) match{
          case true  => min
          case false => max
        }
      case _ =>
        (check(mid, nowi, cnum)) match{
          case true  => binarySearch(min, mid, nowi, cnum)
          case false => binarySearch(mid, max, nowi, cnum)
        }
    }
  }


  var ans = 0L
  var nowi = -1
  breakable {
    for (c <- t) {
      val cnum = c.toInt-97
      val (indice, len) = hoge(cnum)
      if (len == 0) {
        ans = -1
        break
      }
      else {
        if (nowi >= indice(len-1)) {
          ans += sl
          nowi = indice(0)
        }
        else {
          val ind = binarySearch(0, len-1, nowi, cnum)
          nowi = indice(ind)
        }
      }
    }
  }

  ans += nowi + 1
  println(ans)
}

object Sub {
  def print2DimArray[A](mat: Array[Array[A]]): Unit = {
    mat.foreach(lin => println(lin.deep))
  }
}

class InputReader(stream: InputStream) {
  private[this] val reader = new BufferedReader(new InputStreamReader(stream))
  private[this] var tokenizer: StringTokenizer = new StringTokenizer(reader.readLine())
  def next(): String = {
    while (!tokenizer.hasMoreTokens()) {
      tokenizer = new StringTokenizer(reader.readLine())
    }
    tokenizer.nextToken()
  }
}
