const input = require("fs").readFileSync("/dev/stdin", "utf8")

;(input => {

    const lines = input.split('\n')
    const S = lines[0]
    const T = lines[1]

    let count = 0
    for (let i = 0; i < S.length; i++) {
        if (S[i] !== T[i]) {
            count++
        }
    }

    console.log(count)

})(input)
