#include <bits/stdc++.h>
using namespace std;

/******************************* Macros **********************************/

#define F first;
#define S second;
#define eb emplace_back
#define mp make_pair
#define pb push_back
#define MAX(a, b) a = max(a, b)
#define MIN(a, b) a = min(a, b)
#define SQR(x) ((ll)(x) * (x))
#define PERMUTE next_permutation
#define SCD(t) scanf("%d", &t)
#define SCLD(t) scanf("%ld", &t)
#define SCllD(t) scanf("%lld", &t)
#define SCC(t) scanf("%c", &t)
#define SCS(t) scanf("%s", t)
#define SCF(t) scanf("%f", &t)
#define SCLF(t) scanf("%lf", &t)
#define MEM(a, b) memset(a, (b), sizeof(a))
#define fo(i, a) for (ll i = 0; i < a; i++)
#define For(i, a, b) for (ll i = a; i < b; i++)
#define FOR(i, j, k, in) for (ll i = j; i < k; i += in)
#define RFOR(i, j, k, in) for (ll i = j; i >= k; i -= in)
#define TC(t) while (t--)
#define all(name) name.begin(), name.end()
#define rall(name) name.end(), name.begin()
#define alla(arr, sz) arr, arr + sz
#define SIZE(v) (ll) v.size()
#define SORT(v) sort(All(v))
#define REVERSE(v) reverse(All(v))
#define SORTA(arr, sz) sort(AllA(arr, sz))
#define REVERSEA(arr, sz) reverse(AllA(arr, sz))
#define FOREACH(it, l) for (auto it = l.begin(); it != l.end(); it++)
#define IN(A, B, C) assert(B <= A && A <= C)
#define INF 1000000000000000005ll;
#define EPS 1e-9
#define PI 3.1415926535897932384626433832795
#define MOD 1000000007
#define endl "\n"
#define deb(x) cout << #x << " = " << x << endl;

/******************************* Type Definitions **********************************/

typedef long long ll;
typedef pair<ll, ll> pll;
typedef vector<ll> vll;
typedef vector<string> vs;
typedef vector<pll> vpll;
typedef vector<vll> vvll;
typedef map<ll, ll> mapll;
typedef set<ll> setll;
typedef multiset<ll> msetll;
typedef pair<string, string> pss;

/******************************* Function Declarations **********************************/

bool isPowerOfTwo(ll);
bool isPrime(ll);
void swapNum(ll, ll);
ll numOfDigits(ll);
inline string GetString(void);
inline string uppercase(string);
inline string lowercase(string);
inline string IntToString(ll);
inline ll StringToInt(string);
double tick();

/******************************* Solve Cases **********************************/
void solve()
{
    int count = 0;
    string s,t;
    cin>>s>>t;
    fo(i,s.length()){
        if(s[i]!= t[i])
            count++;
    }
    cout<<count<<endl;
}

/******************************* Start of Main **********************************/

int main()
{
// #ifndef ONLINE_JUDGE
//     freopen("input  .txt", "r", stdin);
//     freopen("output.txt", "w", stdout);
// #endif
    ios_base::sync_with_stdio(false);
    cin.tie(NULL);
    cout.tie(NULL);
    ll t = 1;
    //	cin>>t;
    while (t--)
    {
        solve();
    }
    return 0;
    // cout<<"Execution time : "<<tick()<<"\n";
}
/******************************* End of Main Function **********************************/

/******************************* Function Definitions **********************************/

inline string IntToString(ll a)
{
    char x[100];
    sprintf(x, "%lld", a);
    string s = x;
    return s;
}
bool isPrime(ll n)
{
    if (n == 2)
        return true;
    for (int i = 2; i <= sqrt(n); i += 2)
    {
        if (n % 2 == 0)
            return true;
        if (i == 2)
            ++i;
        else
            i += 2;
    }
    return false;
}

bool isPowerOfTwo(int x)
{
    return x && (!(x & (x - 1)));
}

void swapNum(ll &a, ll &b)
{
    a ^= b;
    b ^= a;
    a ^= b;
}

ll numOfDigits(ll N)
{
    return (floor(log10(N)) + 1);
}

inline ll StringToInt(string a)
{
    char x[100];
    ll res;
    strcpy(x, a.c_str());
    sscanf(x, "%lld", &res);
    return res;
}

inline string GetString(void)
{
    char x[1000005];
    scanf("%s", x);
    string s = x;
    return s;
}

inline string uppercase(string s)
{
    int n = SIZE(s);
    fo(i, n) if (s[i] >= 'a' && s[i] <= 'z')
        s[i] = s[i] - 'a' + 'A';
    return s;
}

inline string lowercase(string s)
{
    int n = SIZE(s);
    fo(i, n) if (s[i] >= 'A' && s[i] <= 'Z')
        s[i] = s[i] - 'A' + 'a';
    return s;
}

double tick()
{
    static clock_t oldt, newt = clock();
    double diff = 1.0 * (newt - oldt) / CLOCKS_PER_SEC;
    oldt = newt;
    return diff;
}

Measured memory_bytes: 3800