import Foundation

func readInt() -> Int {
    return Int(readLine()!)!
}

func readString() -> String {
    return readLine()!
}

func readLines(times: Int) -> [String] {
    var array = [String]()
    for _ in 0..<times {
        array.append(readLine()!)
    }
    return array
}

func readSeparatedStrings() -> [String] {
    return readLine()!.split(separator: " ").map({String($0)})
}

func readStringToStrings() -> [String] {
    return readLine()!.map({String($0)})
}

func readSeparatedInts() -> [Int] {
    return readLine()!.split(separator: " ").map({Int($0)!})
}
func readSeparatedDouble() -> [Double] {
    return readLine()!.split(separator: " ").map({Double($0)!})
}

let s = readStringToStrings()
let t = readStringToStrings()

var count: Int = 0
for i in 0..<s.count {
    if !(s[i] == t[i]) {
        count += 1
    }
}

print(count)
