public static void main ( String [ ] args ) {
  Scanner scanner = new Scanner ( System . in ) ;
  String a = scanner . nextLine ( ) ;
  String b = scanner . nextLine ( ) ;
  int seven = 0 , four = 0 , count = 0 ;
  for ( int i = 0 ;
  i < a . length ( ) ;
  i ++ ) {
    if ( a . charAt ( i ) != b . charAt ( i ) ) {
      if ( a . charAt ( i ) == '4' ) four ++ ;
      else seven ++ ;
      count ++ ;
    }
  }
  System . out . println ( count - Math . min ( four , seven ) ) ;
}

public static void main ( String [ ] args ) { Scanner scanner = new Scanner ( System . in ) ; String a = scanner . nextLine ( ) ; String b = scanner . nextLine ( ) ; int seven = 0 , four = 0 , count = 0 ; for ( int i = 0 ; i < a . length ( ) ; i ++ ) { if ( a . charAt ( i ) != b . charAt ( i ) ) { if ( a . charAt ( i ) == '4' ) four ++ ; else seven ++ ; count ++ ; } } System . out . println ( count - Math . min ( four , seven ) ) ; }
(method_declaration (modifiers) type: (void_type) name: (identifier) parameters: (formal_parameters (formal_parameter type: (array_type element: (type_identifier) dimensions: (dimensions)) name: (identifier))) body: (block (local_variable_declaration type: (type_identifier) declarator: (variable_declarator name: (identifier) value: (object_creation_expression type: (type_identifier) arguments: (argument_list (field_access object: (identifier) field: (identifier)))))) (local_variable_declaration type: (type_identifier) declarator: (variable_declarator name: (identifier) value: (method_invocation object: (identifier) name: (identifier) arguments: (argument_list)))) (local_variable_declaration type: (type_identifier) declarator: (variable_declarator name: (identifier) value: (method_invocation object: (identifier) name: (identifier) arguments: (argument_list)))) (local_variable_declaration type: (integral_type) declarator: (variable_declarator name: (identifier) value: (decimal_integer_literal)) declarator: (variable_declarator name: (identifier) value: (decimal_integer_literal)) declarator: (variable_declarator name: (identifier) value: (decimal_integer_literal))) (for_statement init: (local_variable_declaration type: (integral_type) declarator: (variable_declarator name: (identifier) value: (decimal_integer_literal))) condition: (binary_expression left: (identifier) right: (method_invocation object: (identifier) name: (identifier) arguments: (argument_list))) update: (update_expression (identifier)) body: (block (if_statement condition: (parenthesized_expression (binary_expression left: (method_invocation object: (identifier) name: (identifier) arguments: (argument_list (identifier))) right: (method_invocation object: (identifier) name: (identifier) arguments: (argument_list (identifier))))) consequence: (block (if_statement condition: (parenthesized_expression (binary_expression left: (method_invocation object: (identifier) name: (identifier) arguments: (argument_list (identifier))) right: (character_literal))) consequence: (expression_statement (update_expression (identifier))) alternative: (expression_statement (update_expression (identifier)))) (expression_statement (update_expression (identifier))))))) (expression_statement (method_invocation object: (field_access object: (identifier) field: (identifier)) name: (identifier) arguments: (argument_list (binary_expression left: (identifier) right: (method_invocation object: (identifier) name: (identifier) arguments: (argument_list (identifier) (identifier)))))))))