output_description: Print the answer.
  
  * * *
input_description: Input is given from Standard Input in the following format:
  
      
      
      S
      T
attempt: import sys
  
  sys.setrecursionlimit(10**9)
  
  
  # input = sys.stdin.readline    ####
  def int1(x):
      return int(x) - 1
  
  
  def II():
      return int(input())
  
  
  def MI():
      return map(int, input().split())
  
  
  def MI1():
      return map(int1, input().split())
  
  
  def LI():
      return list(map(int, input().split()))
  
  
  def LI1():
      return list(map(int1, input().split()))
  
  
  def LLI(rows_number):
      return [LI() for _ in range(rows_number)]
  
  
  def MS():
      return input().split()
  
  
  def LS():
      return list(input())
  
  
  def LLS(rows_number):
      return [LS() for _ in range(rows_number)]
  
  
  def printlist(lst, k=" "):
      print(k.join(list(map(str, lst))))
  
  
  INF = float("inf")
  # from math import ceil, floor, log2
  # from collections import deque
  # from itertools import combinations as comb, combinations_with_replacement as comb_w, accumulate, product, permutations
  # from heapq import heapify, heappop, heappush
  # import numpy as np    # cumsum
  # from bisect import bisect_left, bisect_right
  
  
  def solve():
      S = LS()
      T = LS()
  
      ans = 0
      for s, t in zip(S, T):
          if s != t:
              ans += 1
  
      print(ans)
  
  
  if __name__ == "__main__":
      solve()
  
problem_description: Statement
  
  Given are strings S and T. Consider changing S to T by repeating the operation
  below. Find the minimum number of operations required to do so.
  
  Operation: Choose one character of S and replace it with a different
  character.
samples: [{"input": "cupofcoffee\n    cupofhottea", "output": "4\n    \n\nWe can achieve the objective in four operations, such as the following:\n\n  * First, replace the sixth character `c` with `h`.\n  * Second, replace the eighth character `f` with `t`.\n  * Third, replace the ninth character `f` with `t`.\n  * Fourth, replace the eleventh character `e` with `a`.\n\n* * *"}, {"input": "abcde\n    bcdea", "output": "5\n    \n\n* * *"}, {"input": "apple\n    apple", "output": "0\n    \n\nNo operations may be needed to achieve the objective."}]