#include<iostream>
#include<vector>
#include<string>
#include<algorithm>
#include<stack>
#include<unordered_set>
#include<cmath>
#include<tuple>
#include<numeric>
#include<iterator>
#include<set>
#include<unordered_map>
#include<map>
#include<queue>
#include<cstring>
#include<stdio.h>
#include<fstream>
#include<iomanip>
#include<functional>
#include<bitset>
#include<chrono>
#include<assert.h>
#include<climits>
//#include<ext/pb_ds/assoc_container.hpp>
//#include<ext/pb_ds/tree_policy.hpp>

#define fastio ios_base::sync_with_stdio(false); cin.tie(NULL); cout.tie(NULL)
#define foru(i , a , b) for(int i = (int)(a) ; i < (int)(b) ; i++)
#define ford(i , a , b) for(int i = (int)(a) ; i >= (int)(b) ; i--)
#define ain(a , n) for(int i = 0 ; i < (int)n ; i++) cin >> a[i]
#define aout(a , n) for(int i = 0 ; i < (int)n ; i++) cout << a[i] << " "; cend
#define M 1000000007
#define mp make_pair
#define mt make_tuple
#define cend cout << "\n"
#define all(x) x.begin() , x.end()
#define aout2(a , n , m) for(ll i = 0 ; i < n ; i++){for(ll j = 0 ; j < m ; j++){cout << a[i][j] << " ";} cout << endl;}
#define ain2(a , n , m) for(ll i = 0 ; i < n ; i++){for(ll j = 0 ; j < m ; j++){cin >> a[i][j];}}
#define ff first
#define ss second
#define mset(a , b) memset(a , b , sizeof(a))
#ifndef ONLINE_JUDGE
#define dbg(a) cerr << #a << ": "; _print(a); cerr << endl;
#else
#define dbg(a) // No more TLEs

#endif

using namespace std;
using namespace std::chrono;
//using namespace __gnu_pbds;
typedef long long ll;
typedef unsigned long long ull;
typedef long double ldb;
typedef vector <int> vi;
typedef vector <ll> vll;
typedef vector <char> vch;
typedef vector <string> vs;
typedef set <ll> sll;
typedef multiset <ll> msll;
typedef pair <ll , ll> pll;
typedef vector <pair <ll , ll>> vpll;
//typedef tree<pair<pair <int, int>, int>, null_type, less<pair<pair<int, int>, int>>, rb_tree_tag, tree_order_statistics_node_update> ordered_set;


void _print(ll t){cerr<<t;}
void _print(int t){cerr<<t;}
void _print(string t){cerr<<t;}
void _print(char t){cerr<<t;}
void _print(ldb t){cerr<<t;}
void _print(double t){cerr<<t;}
void _print(ull t){cerr<<t;}

template <class T, class V> void _print(pair <T, V> p);
template <class T> void _print(vector <T> v);
template <class T> void _print(set <T> v);
template <class T, class V> void _print(map <T, V> v);
template <class T> void _print(multiset <T> v);
template <class T, class V> void _print(pair <T, V> p){cerr<< "{";_print(p.ff);cerr<<",";_print(p.ss);cerr<<"}";}
template <class T> void _print(vector <T> v){cerr<<"[ ";for(T i: v){_print(i);cerr<<" ";}cerr << "]";}
template <class T> void _print(set <T> v){cerr<<"[ ";for(T i: v){_print(i);cerr<<" ";}cerr << "]";}
template <class T> void _print(multiset <T> v){cerr<<"[ ";for(T i: v){_print(i);cerr<<" ";}cerr << "]";}
//void _print(ordered_set &v){cerr<<"[ ";for(int i: v){_print(i);cerr<<" ";}cerr << "]";}
template <class T, class V> void _print(map <T, V> v){cerr<<"[ ";for(auto i: v){_print(i);cerr<<" ";}cerr << "]";}

/*----------------------------- # --- MATH ALGORITHMS --- # -----------------------------*/

template <class T> T gcd(T a , T b){ while(a != 0){T temp = a; a = b % a; b = temp;}return b;}
template <class T> T egcd(T a , T b , T &x , T &y){T gcd , xt , yt;if(a == 0){gcd = b;x = 0 , y = 1;}else {gcd = egcd(b % a , a , xt , yt);x = yt - (b/a)*xt; y = xt;}return gcd;}
template <class T> T expo(T base , T exp , T mod){T res = 1;base = base % mod;while (exp > 0){if (exp & 1)res = (res*base) % mod;exp = exp>>1;base = (base*base) % mod;}return res;}
template <class T> T modinv(T a , T mod){T x , y; egcd<T>(a , mod , x , y);while(x < 0) x += mod; while(x >= mod) x -= mod; return x;}
template <class T> T modinvfermat(T a , T mod){return expo<T>(a , mod - 2 , mod);}
template <class T> bool rev(T a , T b){return a > b;}
template <class T> ll maxpower(T a , T b){ll ans = 0;while(a > 0 && a % b == 0){ans++;a /= b;}return ans;}
template <class T> T mceil(T a, T b){if(a % b == 0) return a/b; else return a/b + 1;}
template <class T> T lcm(T a, T b){return (a*b)/gcd<T>(a, b);}
const ll infl = LLONG_MAX; const int inf = INT_MAX;

/*----------------------------- # --- MAIN CODE --- # -----------------------------*/

void test_case(){
    string s, t; cin >> s >> t;
    ll ans = 0;
    foru(i, 0, s.length()){
        if(s[i] != t[i]) ans++;
    }
    cout << ans;
}

int main() {
    fastio;
#ifndef ONLINE_JUDGE
    freopen("testcase.txt", "r", stdin);
    freopen("error.txt", "w", stderr);
    freopen("output.txt", "w", stdout);
#endif
    int _;
//    cin >> _;
    _ = 1;
    auto t1 = clock();
    while(_--){
        test_case();
    }
    auto t2 = clock();
#ifndef ONLINE_JUDGE
    cerr << "Time: " << (t2 - t1)*(1.0)/CLOCKS_PER_SEC;
#endif
}









Measured memory_bytes: 3840