#include <bits/stdc++.h>
using namespace std;
#define ll                 long long
#define ull                unsigned long long
#define ld                 long double
#define fastio             ios_base::sync_with_stdio(false);cin.tie(NULL);
#define NO                 cout << "NO" << endl
#define YES                cout << "YES" << endl
#define vec                vector<ll>
#define pi                 pair<ll, ll>
#define intarr(arr, n)     ll arr[n]; for (ll i = 0; i < n; i++) cin >> arr[i]
#define intvec(v, n)       for (ll i = 0; i < n; i++) { ll x;cin >> x; v.pb(x);}
#define loop(i, a, b, c)   for (ll i = a; i < b; i += c)
#define pb                 push_back
#define mkp                make_pair
#define ins                insert
#define print(a, n, m)     for (ll i = n; i < m; i++) {  cout << a[i] << " "; }  cout << endl
#define endl               "\n"
#define mod2               998244353
#define mod                1000000007
#define mem(dp, a)         memset(dp, a, sizeof(dp));
#define all(v)             v.begin(), v.end()
#define ump                unordered_map<ll, ll>
#define ff                 first
#define ss                 second
#define PI                 3.14159265358979
#define minh               priority_queue<ll>
#define maxh               priority_queue<ll,vector<ll>,greater<ll>>
#define flush              cout<<flush

//If path exist b/w A and B - BFS, DFS

// Shortest Path - BFS(unweighted), Dijkstra, Bellman-ford
//                 Floyd-Warshall, A*

//To detect negative cycles - Bellman-ford, Floyd-Warshall
//DFS - Connectivity, count connected components,
//      Find Bridges/Articulation points

ll Ceil(ll a, ll b)
{
  if (a % b == 0)
    return a / b;
  else
    return a / b + 1;
}

ll gcd(ll a, ll b)
{
  if (b == 0)
    return a;
  return gcd(b, a % b);
}

ll inv(ll a)
{
  ll p = mod;
  ll b = p - 2, ans = 1;
  for (; b > 0; a = a * a % p, b >>= 1)
    if (b & 1)
      ans = ans * a % p;
  return ans;
}

ll ncrmod(ll n, ll m)
{
  ll p = mod;
  if (m > n)
    return 0;
  ll up = 1, down = 1;
  for (ll i = n - m + 1; i < n + 1; i++)
    up *= i, up %= p;
  for (ll i = 1; i < m + 1; i++)
    down *= i, down %= p;
  return up * inv(down) % p;
}

ll powmod(ll a, ll n)
{
  if (!n)
    return 1;
  ll pt = powmod(a, n / 2);
  pt *= pt, pt %= mod;
  if (n & 1)
    pt *= a, pt %= mod;
  return pt;
}

void factorize(long long int n)
{
  ll sum2 = 0, sum = 0;
  ll count = 0;

  while (!(n % 2)) {
    n >>= 1;
    count++;
  }

  if (count)
  {
    sum2 += count;
  }

  for (long long i = 3; i <= sqrt(n); i += 2) {
    count = 0;
    while (n % i == 0) {
      count++;
      n = n / i;
    }
    if (count)
    {
      if (i & 1)sum += count;
    }
  }
  if (n > 2)
  {
    sum++;
  }
}


map<ll, vec > g;
map<ll, bool> visited;
ll cnt = 0;
void dfs(ll i) {
  visited[i] = true;
  //cout << i << "-> ";
  cnt++;
  for (auto j : g[i]) {
    if (visited[j] == false)
      dfs(j);
  }
}

void bfs(ll s) {
  queue<ll> q;

  visited[s] = true;
  q.push(s);

  while (!q.empty()) {
    ll front = q.front();
    cout << front << " ";
    q.pop();
    for (auto i : g[front]) {
      if (!visited[i]) {
        visited[i] = true;
        q.push(i);
      }
    }
  }
}


void solve()
{
  string s1, s2;
  cin >> s1 >> s2;
  ll count = 0;
  ll n = s1.length();
  for (ll i = 0; i < n; i++) {
    if (s1[i] != s2[i]) count++;
  }
  cout << count;
}

int main()

{
#ifndef ONLINE_JUDGE
  freopen("input.txt", "r", stdin);
  freopen("output.txt", "w", stdout);
#endif

  fastio;
  ll t;
  t = 1;
  //cin >> t;
  while (t--)
  {
    solve();
  }

  cerr << "\nTime elapsed: " << 1000 * clock() / CLOCKS_PER_SEC << "ms\n";

  return 0;
}

Measured memory_bytes: 3888