let S: String = readLine()!
let T: String = readLine()!
var res: Int = 0
var idx: String.Index = S.startIndex

for _ in 1...S.count {
    if S[idx] != T[idx] { res += 1 }
    idx = S.index(after: idx)
}
print(res)	// (๑•ૅㅁ•๑)