#include<bits/stdc++.h>
//One implementation to rule them all?
#define db              double
#define ll              long long int
#define ld              long long double
//#define int           long long int
#define ull             unsigned long long
#define fi              first
#define se              second
#define rep(i,a,n)      for(int i=a;i<n;i++)
#define repr(i,n,b)     for(int i=n;i>=b;i--)
#define endl            '\n'
#define mem(a,b)        memset(a, b, sizeof a)
#define mkp             make_pair
#define pb              push_back
#define max3(a,b,c)     max(a,max(b,c))
#define min3(a,b,c)     min(a,min(b,c))
#define w(t)            int t; cin>>t; while(t--)
#define all(a)          a.begin(), a.end()
#define sz(a)           int((a).size())
#define dbg(x)          cerr << #x << " = " << x << endl;
#define printdb(i)      printf("%.10lf\n",i)
#define isOn(S, j)      (S & (1<<j))
#define setBit(S, j)    (S |= (1<<j))
#define clearBit(S, j)  (S &= ~(1<<j))
#define toggleBit(S, j) (S ^= (1<<j))
#define lowBit(S)       (S & (-S))
#define setAll(S, n)    (S = (1<<n)-1)
#define turnOffLastBit(S) ((S) & (S-1))
#define turnOnLastZero(S) ((S) | (S+1))
//Can use tuples in C++17
using namespace std;
typedef map < int, int > mii;
typedef vector < int > vii;
typedef vector < ll > vll;
typedef vector < vii > vvi;
typedef pair < int,int > pii;
template <class T> using min_heap = priority_queue<T,vector<T>,greater<T> >;
template <class T> using max_heap = priority_queue<T>;
const db PI = 2*acos(0.0);
const int INF = 0x3f3f3f3f;
const ll LINF = (ll)2e18;
db eps       =          0.000001;
ll mod       =          (1e9+7);    //998244353   
void print(vector <int> &arr){
    for(int i=0;i<arr.size();i++)
        cout<<arr[i]<<" ";
    
    cout<<endl;
}
void printll(vector <ll> &arr){
    for(int i=0;i<arr.size();i++)
        cout<<arr[i]<<" ";
    
    cout<<endl;
}

ll ncr(ll n, ll r)
{
    r=min(r,n-r);
    ll A[r],i,j,B[r];
    iota(A,A+r,n-r+1);  
    iota(B,B+r,1);     

    ll g;
    for(i=0;i<r;i++)
    for(j=0;j<r;j++)
    {
        if(B[i]==1)
            break;
        g=__gcd(B[i], A[j] );
        A[j]/=g;
        B[i]/=g;
    }
    ll ans=1;
    for(i=0;i<r;i++)
        ans=(ans*A[i]%mod);
    return ans;
}
const int SIZE=1000010;
bool judge(int a[], int n){
    static int used[SIZE+1];
    for(int i = 1; i <= n; i++) used[i] = 0;
    for(int i = 0; i < n; i++) used[a[i]] = 1;
    for(int i = 1; i <= n; i++) {
        if(!used[i]) return 0;
    }
    return 1;
}
vector <bool> prime(SIZE+1,true);
vii primes;
vii spf(SIZE); 
void sieve(){
    prime[0]=prime[1]=false;
    for(int i=2;i*i<=SIZE;i++){
        if(prime[i]){
            for(int j=i*i;j<=SIZE;j+=i) prime[j]=false;
        }
    }
}
void sievespf() 
{ 
    rep(i,1,SIZE) spf[i]=i;
    for (int i=4; i<SIZE; i+=2) 
        spf[i] = 2; 
    for (int i=3; i*i<SIZE; i++) 
    { 
        if (spf[i] == i) 
        { 
            for (int j=i*i; j<SIZE; j+=i) 
                if (spf[j]==j) 
                    spf[j] = i; 
        } 
    } 
} 
vector<bool> segment(ll L, ll R) {
    ll lim = sqrt(R);
    vector<bool> mark(lim + 1, false);
    vll primes;
    for (ll i = 2; i <= lim; ++i) {
        if (!mark[i]) {
            primes.emplace_back(i);
            for (ll j = i * i; j <= lim; j += i)
                mark[j] = true;
        }
    }

    vector<bool> isPrime(R - L + 1, true);
    for (ll i : primes)
        for (ll j = max(i * i, (L + i - 1) / i * i); j <= R; j += i)
            isPrime[j - L] = false;
    if (L == 1)
        isPrime[0] = false;
    return isPrime;
}
vii cnt(SIZE);
void get(int x) 
{ 
	int temp=x;
    set <int> ret; 
    while (x != 1) 
    { 
        ret.insert(spf[x]); 
        x = x / spf[x]; 
    } 
    cnt[temp]=sz(ret); 
} 
int main(){ 
//CONDITION && cout << "YES" || cout << "NO"; cout << '\n';
//////////////////////////////////////////////////////////////////////
  ios_base::sync_with_stdio(false);
  cin.tie(NULL);
  cout.tie(NULL);
  cerr.tie(NULL);
//For fast IO
///////////////////////////////////////////////////////////////////// 
// Have you thought about it enough?
/////////////////////////////////////////////////////////////////////
//  std::cout.unsetf ( std::ios::floatfield );  // floatfield not set
//  std::cout.precision(10);
//  freopen("input.txt","r",stdin);
//  freopen("output.txt","w",stdout);
    string s,t;
    cin>>s>>t;
    ll ans=0;
    rep(i,0,sz(s)){
    	if(s[i]!=t[i]) ans++;
	}
	cout<<ans<<endl;
    return 0;
}

Measured memory_bytes: 11672