fun main() = Thread(null, ::abc172b, "(^o^)", 128 * 1024 * 1024).apply { start() }.join()

@OptIn(ExperimentalStdlibApi::class)
fun abc172b() {
    val s = readLine()!!
    val t = readLine()!!

    val answer = s.zip(t).count { it.first != it.second }

    println(answer)
}
