#pragma region kyomukyomupurin

/**
 *    author  : 𝒌𝒚𝒐𝒎𝒖𝒌𝒚𝒐𝒎𝒖𝒑𝒖𝒓𝒊𝒏
 *    created : 2020-06-27 23:00:31
 **/

#include <algorithm>
#include <bitset>
#include <cassert>
#include <cctype>
#include <chrono>
#include <cmath>
#include <complex>
#include <deque>
#include <iomanip>
#include <iostream>
#include <map>
#include <numeric>
#include <queue>
#include <random>
#include <set>
#include <stack>
#include <string>
#include <tuple>
#include <utility>
#include <vector>

using namespace std;

using int64 = long long;

template<class T>
inline void eraque(std::vector<T>& vec) {
  vec.erase(std::unique(vec.begin(), vec.end()), vec.end());
  return;
}

template<class T>
inline int lower_position(const std::vector<T>& vec, T value) {
  return static_cast<int>(std::distance(vec.begin(), std::lower_bound(vec.begin(), vec.end(), value)));
}

template<class T>
inline int upper_position(const std::vector<T>& vec, T value) {
  return static_cast<int>(std::distance(vec.begin(), std::upper_bound(vec.begin(), vec.end(), value)));
}

template <class T>
using binary_heap = std::priority_queue<T, std::vector<T>, std::greater<T>>;

template <class T, class U>
std::ostream& operator<<(std::ostream& os, const std::pair<T, U>& p) {
  return os << '(' << p.first << ", " << p.second << ')';
}

template <class Tuple, std::size_t... Is>
void tuple_out(std::ostream& os, const Tuple& tp, std::index_sequence<Is...>) {
  ((os << (Is ? ", " : "(") << std::get<Is>(tp)), ...) << ")";
}

template <class... Args>
std::ostream& operator<<(std::ostream& os, const std::tuple<Args...>& tp) {
  tuple_out(os, tp, std::index_sequence_for<Args...>{});
  return os;
}

template <class T>
std::ostream& operator<<(std::ostream& os, const std::vector<T>& vec) {
  int n = 0;
  for (auto e : vec) os << (n++ ? ", " : "{") << e;
  return os << (n ? "}" : "{}");
}

template <class T, class Compare>
std::ostream& operator<<(std::ostream& os, const std::set<T, Compare>& st) {
  int n = 0;
  for (auto e : st) os << (n++ ? ", " : "{") << e;
  return os << (n ? "}" : "{}");
}

template <class T, class U, class Compare>
std::ostream& operator<<(std::ostream& os, const std::map<T, U, Compare>& mp) {
  int n = 0;
  for (auto e : mp) os << (n++ ? ", " : "{") << e;
  return os << (n ? "}" : "{}");
}

template <class T>
std::istream& operator>>(std::istream& is, std::vector<T>& vec) {
  for (T& e : vec) is >> e;
  return is;
}

template <class T, class U>
std::istream& operator>>(std::istream& is, std::pair<T, U>& p) {
  return is >> p.first >> p.second;
}

template <class Tuple, std::size_t... Is>
void tuple_in(std::istream& is, Tuple& tp, std::index_sequence<Is...>) {
  ((is >> std::get<Is>(tp)), ...);
}

template <class... Args>
std::istream& operator>>(std::istream& is, std::tuple<Args...>& tp) {
  tuple_in(is, tp, std::index_sequence_for<Args...>{});
  return is;
}

#define all(_) begin(_), end(_)
#define rall(_) rbegin(_), rend(_)

#ifdef LOCAL
#define debug(...) cerr << "[" << #__VA_ARGS__ << "]: ", debug_out(__VA_ARGS__)
#else
#define debug(...)
#endif

void debug_out() { std::cerr << '\n'; }

template <class Head, class... Tail>
void debug_out(Head&& head, Tail&&... tail) {
  std::cerr << head;
  if (sizeof...(Tail) != 0) std::cerr << ", ";
  debug_out(std::forward<Tail>(tail)...);
}

#pragma endregion kyomukyomupurin

int main() {
  ios_base::sync_with_stdio(false);
  cin.tie(nullptr);

  string s, t; cin >> s >> t;
  int n = s.size();
  int ans = 0;
  for (int i = 0; i < n; ++i) ans += s[i] != t[i];

  cout << ans << endl;

  return 0;
}


Measured memory_bytes: 3884