import java.util.Scanner

import scala.io.StdIn._
object Main extends App {

  val s = scala.io.StdIn.readLine()
  val t = scala.io.StdIn.readLine()

  def solve(): Int = {
    s.zipWithIndex.foldLeft(0) { case (acc, (char, index)) =>
      if(char == t(index)) acc  else acc + 1
    }
  }

  println(solve())

}
