/*
ID: shihabu1
TASK:
LANG: C++14
*/
#include<bits/stdc++.h>
#include <ext/pb_ds/assoc_container.hpp>
#include <ext/pb_ds/tree_policy.hpp>
//#include <boost/multiprecision/cpp_int.hpp>
//
//using namespace boost::multiprecision;
using namespace __gnu_pbds;
using namespace std;
typedef tree<int, null_type, less_equal<int>, rb_tree_tag, tree_order_statistics_node_update> ordered_set;

/*** Typedef ***/
typedef long long ll;
//typedef int ll;
typedef long long int lli;
typedef unsigned long long ull;
typedef    long double   ld;

//typedef    unordered_set<ll>   usll;
//typedef    unordered_multiset<ll>   umsll;

/*** Loops ***/
#define ffit(i, dat)    for (__typeof(dat.begin()) i = dat.begin(); i != dat.end(); ++i)
#define ff1(i,a,b) for(ll i = a; i < b; i++)
#define ff2(i,a,b) for(ll i = b-1; i >= a; i--)
#define ff3(i,a,b,m) for(ll i = a; i <b; i+=m)
#define ipar(ar,n) ll ar[n]; ff1(i,0,n) cin>>ar[i];
#define opar(ar,n) ff1(i,0,n) cout<<ar[i]<<" ";
#define foRev(num) for(ll i = num - 1; i >= 0; i--)
#define forIn(arr, num) for(ll i = 0; i < num; i++) sc1(arr[i]);
#define forIn1(arr, num) for(ll i = 1; i <= num; i++) sc1(arr[i]);
#define vpnt(ans) for(ll i = 0; i < ans.size(); i++) cout << ans[i] << (i + 1 < ans.size() ? ' ' : '\n');
#define apnt(arr, num) for(ll i = 0; i < num; i++) cout << arr[i] << (i + 1 < num ? ' ' : '\n');

/*** Define Values ***/

#define PI acos(-1.0)
#define eps 1e-7
#define size1 15

/*** STLs ***/
#define cu continue
#define br break
#define rsz resize
#define ins insert
#define ft front
#define bk back
#define eb emplace_back
#define lb lower_bound
#define ub upper_bound
#define pb push_back
#define ff first
#define ss second
#define mp make_pair
#define mem(name, value) memset(name, value, sizeof(name))
#define MN3(n1,n2,n3) min(n1,min(n2,n3))
#define MN4(n1,n2,n3,n4) min(n1,min(n2,min(n3,n4)))
#define MX3(n1,n2,n3) max(n1,max(n2,n3))
#define MX4(n1,n2,n3,n4) max(n1,max(n2,max(n3,n4)))
#define mxar(a,n) *max_element(a,a+n)
#define mnar(a,n) *min_element(a,a+n)
#define arr_sm(a,n) accumulate(a,a+n,0)
#define vc_sm(ve) accumulate(ve.begin(),ve.end(),0)
#define mx_vc(ve) *max_element(ve.begin(),ve.end())
#define mn_vc(ve) *min_element(ve.begin(),ve.end())
//#define endl " \n"

/*** STLs ***/
typedef vector <ll> vll;
#define vvll vector<vll>
typedef set <ll> sll;
typedef multiset <ll> msll;
//typedef multimap <ll> mpll;
typedef queue <ll> qll;
typedef map <ll, ll> mll;
typedef pair <ll, ll> pll;
typedef vector <pair <ll, ll> > vpll;
typedef priority_queue <pair <ll, ll> > pqpll;
#define maxpq priority_queue<int>
#define minpq priority_queue<int, vector<int>, greater<int> >
#define ml unordered_map<ll,ll>
///typedef    unordered_multiset<int>   umsi;
typedef    unordered_set<ll>   us;


///vector<vector<int>> v(10, vector<int>(20,500)); 2d vector initialization. of 10 rows and 20 columns, with value 500.

/*** Sorts ***/
#define czero(n)                    __builtin_popcountll(n) // count the number of 1's in the bit representation of a number
#define cenzero(n)                  __builtin_ctzll(n) // count the number of zereos from the end of the bit representation of a number until a 1
#define countbegzero(n)             __builtin_clzxll(n)
#define checkparity(n)              __builtin_parityll(n)// checks whether the number of bits are even or odd
#define all(v) (v).begin(), (v).end()
#define rev(v) reverse(all(v))
#define srt(v) sort(all(v))
#define srtgrt(v) sort(all(v), greater<ll>())
#define prsrt greater<pair<int,int>>()
/*** Some Prints ***/
#define ip(n) ll n; cin>>n;
#define ipp(n,k) ll n; cin>>n; ll k; cin>>k;
#define ip3(n,m,k) ll n; cin>>n;ll m;cin>>m; ll k; cin>>k;
#define kl    '\n'
#define no cout << "NO" << '\n'
#define yes cout << "YES" << '\n'
#define case cout << "Case " << t++ << ": ";
#define ps(x,y)         fixed<<setprecision(y)<<x
#define inf             1e18
#define dbg(x) cout << '>' << #x << ':' << x << kl;
#define trc1(x)                   cerr<<#x<<": "<<x<<kl
#define trc2(x, y)                cerr<<#x<<": "<<x<<" | "<<#y<<": "<<y<<kl
#define trc3(x, y, z)             cerr<<#x<<":" <<x<<" | "<<#y<<": "<<y<<" | "<<#z<<": "<<z<<kl
#define trc4(a, b, c, d)          cerr<<#a<<": "<<a<<" | "<<#b<<": "<<b<<" | "<<#c<<": "<<c<<" | "<<#d<<": "<<d<<kl
#define trc5(a, b, c, d, e)       cerr<<#a<<": "<<a<<" | "<<#b<<": "<<b<<" | "<<#c<<": "<<c<<" | "<<#d<<": "<<d<<" | "<<#e<< ": "<<e<<kl
#define trc6(a, b, c, d, e, f)    cerr<<#a<<": "<<a<<" | "<<#b<<": "<<b<<" | "<<#c<<": "<<c<<" | "<<#d<<": "<<d<<" | "<<#e<< ": "<<e<<" | "<<#f<<": "<<f<<kl
#define w(x)             ll x; cin>>x; while(x--)
bool isPtSquare(long double x)
{
    long double sr = sqrt(x);
    return ((sr - floor(sr)) == 0);
}

ll facts(ll n,ll mod)
{
	ll prod=1;
	for(ll i=1;i<=n;i++)
	{
		prod=(prod*i)%mod;
	}
	return prod;
}

ll binpow(ll a, ll b, ll mod){
	ll ans = 1;
	while(b){
		if(b&1) ans*=a;
		a*=a;
		ans%=mod;
		a%=mod;
		b/=2;
	}
	return ans;
}
ll mod = 1e9+7;
vector<ll> factors(ll n){ // returns all factors of a given number
    ll lim = sqrt(n);
    vector<ll> f;
    for(int i = 1; i <= lim; i++){
        if(n % i == 0){
            f.push_back(i);
            f.push_back(n / i);
            if(i*i == n){
                f.pop_back();
            }
        }
    }
    return f;
}

ll ceilAB(ll a, ll b){
    return (a + b - 1) / b;
}
ll bigmod(ll n,ll pow)
{
    if(pow==0)
        return 1;
    if(pow==1)
        return n%mod;

    ll ans=bigmod(n,pow/2);
    ans=(ans*ans)%mod;

    if(pow%2==1)
    {
        ans=(ans*n)%mod;
    }
    return ans%mod;
}

const int mxn = 1e3;

ll fact[mxn + 1];
void calcfac(ll n, ll mod = 2e18){
	fact[0]  = 1;
	for(int i = 1; i<=n;++i){
		fact[i] = fact[i-1]*i;
		fact[i] %= mod;
	}
}

ll nCr(ll p, ll q, ll mod = 2e18){
	ll val = fact[p];
	ll invfact = fact[q]*fact[p-q];
	val%=mod;
	invfact%=mod;
	val*=binpow(invfact, mod - 2, mod);
	return val%mod;
}


ll nPr(ll p, ll q, ll mod = 2e18){
	ll val = nCr(p, q, mod);
	val*=fact[q];
	val%=mod;
	return val;
}

bool isprime(int n)
{
    if (n <= 1)
        return false;
    if (n <= 3)
        return true;
    if (n % 2 == 0 || n % 3 == 0)
        return false;
    for (int i = 5; i * i <= n; i += 6)
    {
        if ((n % i == 0) || (n % (i + 2) == 0))
            return false;
    }
    return true;
}
ll power(ll x, ll y)
{
    ll temp;
    if(y == 0)
        return 1;
    temp = power(x, y / 2);
    if (y % 2 == 0)
        return temp * temp;
    else
    {
        if(y > 0)
            return (x * temp * temp);
        else
            return ((temp * temp) / x);
    }
}

//ll pmod(ll a,ll b){ll res=1;a%=mod;assert(b>=0);for(; b; b>>=1){if(b&1)res=res*a%mod;a=a*a%mod;}return res;}
//ll expo(ll x, ll y){ ll res = 1; x = x % mod;  while (y > 0) { if (y & 1)res = (res*x) % mod; y = y>>1;x = (x*x) % mod;}return res;}
//void matmul(ll a[][2], ll b[][2]) { ll tmp[2][2]; for(int i=0; i<2; i++) { for(int j=0; j<2; j++) { tmp[i][j] = 0; for(int k=0; k<2; k++) tmp[i][j] = (tmp[i][j] + a[i][k]*b[k][j]) % mod; }} for(int i=0; i<2; i++) for(int j=0; j<2; j++) a[i][j] = tmp[i][j]; }
//ll fibo(int n)    // returns nth fibonacci number, also S(n) = f(n+2)-1
//{ if(n == 0) return 0; else if(n == 1) return 1; ll T[2][2] = { {0, 1} , {1, 1} }; ll res[2][2] = { {1, 0}, {0,1} }; n--; while(n) { if(n & 1) matmul(res, T); n >>= 1; matmul(T, T); } return res[1][1]; }

#define go(i, a) for (auto i : a)
#define go1(it, v) for(auto it = v.begin(); it != v.end(); ++it)
#define mk(arr,n,type) type *arr=new type[n];
#define sz(obj) (int(obj.size()))
#define ipve(vc,n) vll vc(n); ff1(i,0,n){cin>>vc[i];}
#define ipvc(vc,n) vll vc; ff1(i,0,n){ip(x);vc.pb(x);}
#define depressed()                    ios_base::sync_with_stdio(false);cin.tie(NULL);cout.tie(NULL)
//bool ans = all_of(arr, arr + 6, [](int x) {return x & 1; } );
const double pi = 3.141592653589793238460;
ll cbtr(ll n,ll m)
{
    ll sm = 1;
    ff1(i,1,m+1)
    {
        sm*=(n-i+1);
        sm/=i;
    }
    return sm;
}
//string a="cdefghijklmnopqrstuvwxyz";
ld f(ld n)
{
    ld sm = 1;
    ff1(i,1,n+1)
    {
        sm*=i;
    }
    return sm;
}
ld pc(ld n, ld k)
{
    ld sm = f(n)/f(n-k);
    return sm;
}
vll prime;
void seive(ll n)
{
    prime.resize(n+1,1);
    iota(prime.begin(), prime.end(), 0);
    prime[0] = 0, prime[1] = 0;
    for (int i = 2; i*i <= n; i++)
        if (prime[i] == i)
            for (int j = i * i; j <= n; j += i)
                prime[j] = i;
}
map< ll, ll > prime_factor(ll n) {
  map< ll, ll > ret;
  for(ll i = 2; i * i <= n; i++) {
    while(n % i == 0) {
      ret[i]++;
      n /= i;
    }
  }
  if(n != 1) ret[n] = 1;
  return ret;
}
bool p2(ll n)
{
    if(n==0)
        return false;

    return (ceil(log2(n)) == floor(log2(n)));
}
#define cer cerr << "Time : " << 1000 * ((double)clock()) / (double)CLOCKS_PER_SEC << "ms\n";

ll modInverse(ll n, ll m){
    return binpow(n, m - 2, m);
}
void shape_of_voice()
{
 /// valo hoia gesi
 string s,s1;
 cin>>s>>s1; ll ct = 0;
 ff1(i,0,sz(s))
 {
     if(s[i] != s1[i]) ct++;
 }
 cout<<ct<<kl;
}

int main()
{
//     ofstream cout ("ride.out");
//     ifstream cin ("ride.in");
    depressed();
  ll t = 1;
  //cin>>t;
  while(t--)
  {
     shape_of_voice();
  }
  return 0;
}

/// OPM ROCKS         8
/***The One Punch Man Workout Routine
100 Push-Ups
100 Sit-Ups
100 Squats
10KM Running (that's 6.2 miles)
Repeat 7 days a week. That's it!***/


Measured memory_bytes: 3808