extension String {
    /// lengthに指定した文字数で文字列を分割する
    func splitInto(_ length: Int) -> [String] {
        var str = self
        for i in 0 ..< (str.count - 1) / max(length, 1) {
            str.insert(",", at: str.index(str.startIndex, offsetBy: (i + 1) * max(length, 1) + i))
        }
        return str.components(separatedBy: ",")
    }
}

import Foundation
let S = readLine()!.splitInto(1)
let T = readLine()!.splitInto(1)

var count = 0
for (i, s) in S.enumerated() {
    if s != T[i] {
        count += 1
    }
}

print(count)
