/**
 *    author:   K.R.Surrya  
 *    created:  27.06.2020 17:19:30
**/
//~ ~~ ~~~~ ~~~~~~~~   
#include<bits/stdc++.h>
using namespace std; 
using lint  =                           long long int;
using pint  =                           pair<int, int>;
using plint =                           pair<lint, lint>;
#define arr                             array
#define vi                              vector<int>
#define vli                             vector<lint>
#define pb                              push_back
#define ALL(x)                          begin(x),end(x)
#define inf                             (1LL<63)-1
#define MOD                             1000000007
#define SZ(x)                           ((lint)(x).size())
#define                                 FOR(i, begin, end) for(int i=(begin),i##_end_=(end);i<i##_end_;i++)
#define                                 IFOR(i, begin, end) for(int i=(end)-1,i##_begin_=(begin);i>=i##_begin_;i--)
#define                                 REP(i, n) FOR(i,0,n)
#define                                 IREP(i, n) IFOR(i,0,n)
#define                                 f_ip   ios_base::sync_with_stdio(false); cin.tie(NULL);
#define ZERO(a)                         fill(ALL(a),0)
#define lastBit(n)                      31-__builtin_clz(n) + 1 //32 bit integers, 1-based indexing.
#define firstBit(n)                     __builtin_ctz((n&(-n))) + 1
struct fast_ios                         { fast_ios(){ cin.tie(0); ios::sync_with_stdio(false); cout << fixed << setprecision(20); }; } fast_ios_;
template<typename T>                    istream &operator>>(istream &is, vector<T> &vec){ for (auto &v : vec) is >> v; return is; }
template<typename T>                    bool chmax(T &m, const T q) { if (m < q) {m = q; return true;} else return false; }
template<typename T>                    bool chmin(T &m, const T q) { if (q < m) {m = q; return true;} else return false; }
mt19937                                 rng(chrono::steady_clock::now().time_since_epoch().count());



        /* ~Debugging~ */         
      /*~~~~~~~~~~~~~~~~~*/       
#define LOCAL
#define sim template <class c
#define ris return *this
#define dor > deb &operator<<
#define eni(x)                                                                  \
    sim > typename enable_if<sizeof dud<c>(0) x 1, deb &>::type operator<<(c i) \
    {
sim > struct rge
{
    c b, e;
};
sim > rge<c> range(c i, c j) { return rge<c>{i, j}; }
sim > auto dud(c *x) -> decltype(cerr << *x, 0);
sim > char dud(...);
struct deb
{
#ifdef LOCAL
    ~deb()
    {
        cerr << endl;
    }
    eni(!=) cerr << boolalpha << i;
    ris;
} eni(==) ris << range(begin(i), end(i));
}
sim, class b dor(pair<b, c> d)
{
    ris << "(" << d.first << ", " << d.second << ")";
}
sim dor(rge<c> d)
{
    *this << "[";
    for (auto it = d.b; it != d.e; ++it)
        *this << ", " + 2 * (it == d.b) << *it;
    ris << "]";
}
#else
    sim dor(const c &)
    {
        ris;
    }
#endif
}
;
#define what(...) " [" << #__VA_ARGS__ ": " << (__VA_ARGS__) << "] "
// -DLOCAL



      /*  ~magic~ */            
    /*~~~~~~~~~~~~~~~*/           
#define magic(args...) { string _s = #args; replace(_s.begin(), _s.end(), ',', ' '); stringstream _ss(_s); istream_iterator<string> _it(_ss); err(_it, args); }
void err(istream_iterator<string> it)  { return ;}
template<typename T, typename... Args>
void err(istream_iterator<string> it, T a,Args... args)
{
cerr << *it << " = " << a <<endl;
err(++it,args...);   //args is going to end.
}



    /* ~driver~ */
    /*~~~~~~~~~~*/
void solve() {
     string s;
     cin >> s;
     string t;cin >> t;
     int n = (int)s.size();
     int ret =0 ;
     REP(i,n) { 
         if(s[i]!=t[i]) ++ret;
     }
     cout << ret << '\n';
}


int main()
{   
     #if 0
     freopen("input.txt", "r", stdin);
     freopen("output.txt", "w", stdout);
     #endif

     int T=1;
     //cin>>T;
     for(int tt=1;tt<=T;++tt) {
         solve();
     }

    return 0;
}


     /* ~Modulus functions~ */
    /*~~~~~~~~~~~~~~~~~~~~~~~*/
lint pow_mod(lint base,lint expo) { 
   lint ret = 1;
   for(;expo;) { 
      if(expo&1)  ret = (ret*base)%MOD; 

      expo = (expo>>1);
      base = (base*base)%MOD;
   }
   return ret;
}


Measured memory_bytes: 3792