public static void main ( String args [ ] ) {
  Scanner in = new Scanner ( System . in ) ;
  String s = in . next ( ) ;
  int c4 = 0 , c7 = 0 ;
  for ( int i = 0 ;
  i < s . length ( ) ;
  i ++ ) {
    if ( s . charAt ( i ) == '4' ) c4 ++ ;
    else if ( s . charAt ( i ) == '7' ) c7 ++ ;
  }
  if ( c4 == 0 && c7 == 0 ) System . out . println ( "-1" ) ;
  else if ( c7 > c4 ) System . out . println ( "7" ) ;
  else System . out . println ( "4" ) ;
}

public static void main ( String args [ ] ) { Scanner in = new Scanner ( System . in ) ; String s = in . next ( ) ; int c4 = 0 , c7 = 0 ; for ( int i = 0 ; i < s . length ( ) ; i ++ ) { if ( s . charAt ( i ) == '4' ) c4 ++ ; else if ( s . charAt ( i ) == '7' ) c7 ++ ; } if ( c4 == 0 && c7 == 0 ) System . out . println ( " - 1" ) ; else if ( c7 > c4 ) System . out . println ( "7" ) ; else System . out . println ( "4" ) ; }
(method_declaration (modifiers) type: (void_type) name: (identifier) parameters: (formal_parameters (formal_parameter type: (type_identifier) name: (identifier) dimensions: (dimensions))) 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: (integral_type) 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: (character_literal))) consequence: (expression_statement (update_expression (identifier))) alternative: (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))))))) (if_statement condition: (parenthesized_expression (binary_expression left: (binary_expression left: (identifier) right: (decimal_integer_literal)) right: (binary_expression left: (identifier) right: (decimal_integer_literal)))) consequence: (expression_statement (method_invocation object: (field_access object: (identifier) field: (identifier)) name: (identifier) arguments: (argument_list (string_literal)))) alternative: (if_statement condition: (parenthesized_expression (binary_expression left: (identifier) right: (identifier))) consequence: (expression_statement (method_invocation object: (field_access object: (identifier) field: (identifier)) name: (identifier) arguments: (argument_list (string_literal)))) alternative: (expression_statement (method_invocation object: (field_access object: (identifier) field: (identifier)) name: (identifier) arguments: (argument_list (string_literal))))))))