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#include <bits/stdc++.h>
using namespace std;
#define int long long 
#define IOS ios_base::sync_with_stdio(false);cin.tie(NULL);cout.tie(NULL);
#define vi vector <int>
#define vp vector <pair<int,int>>
#define vpp vector <pair<int,pair<int,int>>>
#define seti set<int>
#define fs(it,a) for(auto it=a.begin();it!=a.end();it++)
#define q " "
#define pb push_back
#define pob pop_back
#define mp make_pair
#define all(x) x.begin(),x.end()
#define f(x,y,z) for(x=y;x<z;x++)
#define si size()
#define M 1000000007  
//Use (k%M+m)%m always where k is any no
#define ee "\n"
#define re return 



//Author Rahul Sannigrahi

int countdigit(int n);
int power(int x,int y);

int eg(int a,int b);
int maxr(vi v,int k);
bool isprime(int n); 
vector<int> aaja(int n);
vector<int> soe(int n); 

vector<int> aaja(int n)
{
    int i,j;
    vi v;
    f(i,0,n)
    {
        cin>>j;
        v.pb(j);
    }
    re v;
}
 
int mjekrtehai()
{
    string s,t;
    int c=0,i;
    cin>>s>>t;
    if(s==t)
    cout<<0<<ee;
    else{
    f(i,0,s.si)
    if(s[i]!=t[i])
    c++;
    cout<<c<<ee;}
   re 0;
}
 
int32_t main()
{
    IOS
    int t=1;
    //cin>>t;
    while(t--)
    mjekrtehai();
    return 0;
}
 

int eg(int a,int b)
{
    if(a==0)
    return b;
    else
    return eg(b%a,a);
}

vector<int> soe(int n) 
{ 
    vi prime(n+1,1); 
    
    for (int p=2; p*p<=n; p++) 
    { 
        if (prime[p] == 1) 
        { 
            for (int i=p*p; i<=n; i += p) 
                prime[i] = 0; 
        } 
    }

    return prime;
} 


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=i+6) 
        if ((n%i==0)|| n%(i+2)==0) 
           return false; 
  
    return true; 
} 
//fill(all(v,1)); //fill v and vector with 1 or any no you want
//but firslty you have to declare size of vector and also array
//v.back()  gives the last element value of vector
//v.clear to erase the entire vector
//set and multiset me erase kr skta hai .erase set
//long long =7;
//int cnt=__builtin_popcountll(); //pop_count ll here ll for long long
//__builtin_popcountll will return the no of ones in set
int power(int x,int y)
{
    int res=1;
    
    while(y>0)
    {
       if(y&1)
       res=res*x;
       
       y=y>>1;
       x*=x;
    }
    re res;
}    

int countdigit(int n)
{
    return floor(log10(n)+1);
}

int maxr(vector<int> arr, int k) 
{ 
    //gives the max repeating element value
    // in range of k where 0<=k<n
    for (int i = 0; i< arr.si; i++) 
        arr[arr[i]%k] += k; 
  
    int max = arr[0], result = 0; 
    for (int i = 1; i < arr.si; i++) 
    { 
        if (arr[i] > max) 
        { 
            max = arr[i]; 
            result = i; 
        } 
    } 
    return result; 
} 










Measured memory_bytes: 3836