
fun main(args: Array<String>) {
    // var numberTests = readLine()!!.toInt()
    // var results = mutableListOf<String>()

    // for (i in 0..numberTests-1) {
    var s = readLine()!!
    var t = readLine()!!

    
    val result = experiment(s, t)
    // results.add(result)
    // }

    // for (result in results) {
        println(result)
    // }
}

fun experiment(s: String, t: String) : String {

    var result = 0

    val charsS = s.split("").filter { it != "" }
    val charsT = t.split("").filter { it != "" }

    for (i in 0..charsS.size-1) {
        if (charsS[i] != charsT[i]) result++
    }

    return result.toString()
}