// abc172-b
object Main extends App {
    val s = io.StdIn.readLine
    val t = io.StdIn.readLine

    def rec(count: Int, list1: List[Char], list2: List[Char]): Int = (list1, list2) match {
        case (Nil, Nil) => count
        case (head1::tail1, head2::tail2) => {
            if (head1 != head2) rec(count+1, tail1, tail2)
            else rec(count, tail1, tail2)
        }
    }

    val result = rec(0, s.toList, t.toList)
    println(result)
}