#include <bits/stdc++.h>
#include <boost/range/irange.hpp>
#define RANGE_1(e) (boost::irange(0,(e)))
#define RANGE_2(s,e) (boost::irange((s),(e)))
#define RANGE_3(s,e,step) (boost::irange((s),(e),(step)))
#define RANGE_SELECTER(_1,_2,_3,SELECT,...) SELECT
#define range(...) RANGE_SELECTER(__VA_ARGS__, RANGE_3, RANGE_2, RANGE_1) (__VA_ARGS__)
#define guard(x) if(x);
#define CINS(x) for(auto&& AJNAD:(x))cin>>AJNAD
#define ALL(x) (x).begin(),(x).end()
#define RALL(x) (x).rbegin(),(x).rend()
#define CALL(x) (x).cbegin(),(x).cend()
#define MAX(x) *max_element(ALL(x))
#define MIN(x) *min_element(ALL(x))
#define BIT(n) (1LL<<(n))
#define MOD 1000000007

using namespace std;
using lint = long long;

// template<class T>class irange{private:struct I{T x;T operator*(){return x;}bool operator!=(I&lhs){return x<lhs.x;}void operator++(){++x;}};I i,n;public:irange(T i,T n):i({i}),n({n}){}I&begin(){return i;}I&end(){return n;}};
// template<class T>class srange{private:struct I{T x,s;T operator*(){return x;}bool operator!=(I&lhs){if(s<(T)0)return x>lhs.x;return x<lhs.x;}void operator++(){x=x+s;}};I i,n;public:srange(T i,T n,T s):i({i,s}),n({n,s}){}I&begin(){return i;}I&end(){return n;}};
// template<class T>irange<T>range(T n){return irange(0,n);}template<class T>irange<T>range(T i,T n){return irange(i,n);}template<class T>srange<T>range(T i,T n,T s){return srange(i,n,s);}
template<class T>bool amax(T &a,const T &b){if(a<b){a=b;return true;}return false;}
template<class T>bool amin(T &a,const T &b){if(a>b){a=b;return true;}return false;}

template<int M> struct modint {
    lint val;
    constexpr modint(lint v = 0)noexcept:val(v%M){if(val<0)val+=M;}
    constexpr int getM(){return M;}
    constexpr modint operator-()const noexcept{return val?M-val:0;}
    constexpr modint operator+(const modint& r)const noexcept{return modint(*this)+=r;}
    constexpr modint operator-(const modint& r)const noexcept{return modint(*this)-=r;}
    constexpr modint operator*(const modint& r)const noexcept{return modint(*this)*=r;}
    constexpr modint operator/(const modint& r)const noexcept{return modint(*this)/=r;}
    constexpr modint& operator+=(const modint& r)noexcept{val+=r.val;if(val>=M)val-=M;return *this;}
    constexpr modint& operator-=(const modint& r)noexcept{val-=r.val;if(val<0)val+=M;return *this;}
    constexpr modint& operator*=(const modint& r)noexcept{val=val*r.val%M;return *this;}
    constexpr modint& operator/=(const modint& r)noexcept{lint a=r.val,b=M,u=1,v=0;while(b){lint t=a/b;a-=t*b;swap(a,b);u-=t*v;swap(u,v);}val=val*u%M;if(val<0)val+=M;return *this;}
    constexpr bool operator==(const modint& r)const noexcept{return this->val==r.val;}
    constexpr bool operator!=(const modint& r)const noexcept {return this->val!=r.val;}
    friend constexpr istream& operator>>(istream &is,modint<M>& x)noexcept{return is>>x.val;}
    friend constexpr ostream& operator<<(ostream &os,const modint<M>& x)noexcept{return os<<x.val;}
    friend constexpr modint<M> Mpow(const modint<M> &a,lint n)noexcept{if(n == 0)return 1;auto t=Mpow(a,n/2);t=t*t;if(n&1)t=t*a;return t;}
};

struct initialize{initialize(){cin.tie(nullptr);ios::sync_with_stdio(false);};}init;

int main(){
    /* Code Area */
    string s, t;
    cin >> s >> t;

    int sum = 0;

    for (int i : range((int)s.size())) {
        sum += s[i] == t[i] ? 0 : 1;
    }

    cout << sum << endl;
}


Measured memory_bytes: 3740