import java.io.PrintWriter
import java.util.StringTokenizer

fun main() {

    fun PrintWriter.solve() {
        var s = next()
        var t = next()

        var ans = s.zip(t).filter { it.first != it.second }.count()
        println(ans)

    }

    writer.solve()
    writer.flush()


}


private val reader = System.`in`.bufferedReader()
private val writer = PrintWriter(System.out, false)

private var tokenizer: StringTokenizer = StringTokenizer("")

private fun next(): String {
    while (tokenizer.hasMoreTokens().not()) tokenizer = StringTokenizer(reader.readLine())
    return tokenizer.nextToken()
}

private fun nextInt() = next().toInt()
private fun nextLong() = next().toLong()
private fun nextDouble() = next().toDouble()
private fun nextLine() = reader.readLine()

