#include <stdio.h>
#include <string.h>

int main()
{
  int i;
  char s1[1000];
  char s2[1000];
  char c;
  for(i=0;i<1000;i++){
    scanf("%c",&c);
    if ( c == '\n'){
      s1[i] = '\0';
      break;
    }
    else
      s1[i] = c;
  }
  
  for(i=0;i<1000;i++){
    scanf("%c",&c);
    if ( c == '\n'){
      s2[i] = '\0';
      break;
    }
    else
      s2[i] = c;
  }

  int cnt =0;
  for(i=0;i<strlen(s2);i++){
    if (s1[i] != s2[i]) cnt++;
  }

  printf("%d",cnt);
  return 0;
}
    