public static void main ( String [ ] args ) throws IOException {
  BufferedReader br = new BufferedReader ( new InputStreamReader ( System . in ) ) ;
  int n = Integer . parseInt ( br . readLine ( ) ) ;
  String [ ] ip = br . readLine ( ) . split ( " " ) ;
  int c1 = 0 , c2 = 0 , c3 = 0 , c = 0 ;
  for ( int i = 0 ;
  i < n ;
  i ++ ) {
    if ( Integer . parseInt ( ip [ i ] ) == 4 ) c = c + 1 ;
    else if ( Integer . parseInt ( ip [ i ] ) == 1 ) c1 = c1 + 1 ;
    else if ( Integer . parseInt ( ip [ i ] ) == 2 ) c2 = c2 + 1 ;
    else if ( Integer . parseInt ( ip [ i ] ) == 3 ) c3 = c3 + 1 ;
  }
  c = c + c3 ;
  c1 = ( c3 >= c1 ) ? 0 : c1 - c3 ;
  if ( c2 % 2 == 0 ) {
    c = c + ( c2 / 2 ) ;
    c = c + ( c1 % 4 == 0 ? c1 / 4 : ( c1 / 4 ) + 1 ) ;
  }
  else {
    c2 = ( c2 * 2 ) + c1 ;
    c = c + ( c2 % 4 == 0 ? c2 / 4 : ( c2 / 4 ) + 1 ) ;
  }
  System . out . println ( c ) ;
}

public static void main ( String [ ] args ) throws IOException { BufferedReader br = new BufferedReader ( new InputStreamReader ( System . in ) ) ; int n = Integer . parseInt ( br . readLine ( ) ) ; String [ ] ip = br . readLine ( ) . split ( " ▁ " ) ; int c1 = 0 , c2 = 0 , c3 = 0 , c = 0 ; for ( int i = 0 ; i < n ; i ++ ) { if ( Integer . parseInt ( ip [ i ] ) == 4 ) c = c + 1 ; else if ( Integer . parseInt ( ip [ i ] ) == 1 ) c1 = c1 + 1 ; else if ( Integer . parseInt ( ip [ i ] ) == 2 ) c2 = c2 + 1 ; else if ( Integer . parseInt ( ip [ i ] ) == 3 ) c3 = c3 + 1 ; } c = c + c3 ; c1 = ( c3 >= c1 ) ? 0 : c1 - c3 ; if ( c2 % 2 == 0 ) { c = c + ( c2 / 2 ) ; c = c + ( c1 % 4 == 0 ? c1 / 4 : ( c1 / 4 ) + 1 ) ; } else { c2 = ( c2 * 2 ) + c1 ; c = c + ( c2 % 4 == 0 ? c2 / 4 : ( c2 / 4 ) + 1 ) ; } System . out . println ( c ) ; }
(method_declaration (modifiers) type: (void_type) name: (identifier) parameters: (formal_parameters (formal_parameter type: (array_type element: (type_identifier) dimensions: (dimensions)) name: (identifier))) (throws (type_identifier)) body: (block (local_variable_declaration type: (type_identifier) declarator: (variable_declarator name: (identifier) value: (object_creation_expression type: (type_identifier) arguments: (argument_list (object_creation_expression type: (type_identifier) arguments: (argument_list (field_access object: (identifier) field: (identifier)))))))) (local_variable_declaration type: (integral_type) declarator: (variable_declarator name: (identifier) value: (method_invocation object: (identifier) name: (identifier) arguments: (argument_list (method_invocation object: (identifier) name: (identifier) arguments: (argument_list)))))) (local_variable_declaration type: (array_type element: (type_identifier) dimensions: (dimensions)) declarator: (variable_declarator name: (identifier) value: (method_invocation object: (method_invocation object: (identifier) name: (identifier) arguments: (argument_list)) name: (identifier) arguments: (argument_list (string_literal))))) (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)) 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: (identifier)) update: (update_expression (identifier)) body: (block (if_statement condition: (parenthesized_expression (binary_expression left: (method_invocation object: (identifier) name: (identifier) arguments: (argument_list (array_access array: (identifier) index: (identifier)))) right: (decimal_integer_literal))) consequence: (expression_statement (assignment_expression left: (identifier) right: (binary_expression left: (identifier) right: (decimal_integer_literal)))) alternative: (if_statement condition: (parenthesized_expression (binary_expression left: (method_invocation object: (identifier) name: (identifier) arguments: (argument_list (array_access array: (identifier) index: (identifier)))) right: (decimal_integer_literal))) consequence: (expression_statement (assignment_expression left: (identifier) right: (binary_expression left: (identifier) right: (decimal_integer_literal)))) alternative: (if_statement condition: (parenthesized_expression (binary_expression left: (method_invocation object: (identifier) name: (identifier) arguments: (argument_list (array_access array: (identifier) index: (identifier)))) right: (decimal_integer_literal))) consequence: (expression_statement (assignment_expression left: (identifier) right: (binary_expression left: (identifier) right: (decimal_integer_literal)))) alternative: (if_statement condition: (parenthesized_expression (binary_expression left: (method_invocation object: (identifier) name: (identifier) arguments: (argument_list (array_access array: (identifier) index: (identifier)))) right: (decimal_integer_literal))) consequence: (expression_statement (assignment_expression left: (identifier) right: (binary_expression left: (identifier) right: (decimal_integer_literal)))))))))) (expression_statement (assignment_expression left: (identifier) right: (binary_expression left: (identifier) right: (identifier)))) (expression_statement (assignment_expression left: (identifier) right: (ternary_expression condition: (parenthesized_expression (binary_expression left: (identifier) right: (identifier))) consequence: (decimal_integer_literal) alternative: (binary_expression left: (identifier) right: (identifier))))) (if_statement condition: (parenthesized_expression (binary_expression left: (binary_expression left: (identifier) right: (decimal_integer_literal)) right: (decimal_integer_literal))) consequence: (block (expression_statement (assignment_expression left: (identifier) right: (binary_expression left: (identifier) right: (parenthesized_expression (binary_expression left: (identifier) right: (decimal_integer_literal)))))) (expression_statement (assignment_expression left: (identifier) right: (binary_expression left: (identifier) right: (parenthesized_expression (ternary_expression condition: (binary_expression left: (binary_expression left: (identifier) right: (decimal_integer_literal)) right: (decimal_integer_literal)) consequence: (binary_expression left: (identifier) right: (decimal_integer_literal)) alternative: (binary_expression left: (parenthesized_expression (binary_expression left: (identifier) right: (decimal_integer_literal))) right: (decimal_integer_literal)))))))) alternative: (block (expression_statement (assignment_expression left: (identifier) right: (binary_expression left: (parenthesized_expression (binary_expression left: (identifier) right: (decimal_integer_literal))) right: (identifier)))) (expression_statement (assignment_expression left: (identifier) right: (binary_expression left: (identifier) right: (parenthesized_expression (ternary_expression condition: (binary_expression left: (binary_expression left: (identifier) right: (decimal_integer_literal)) right: (decimal_integer_literal)) consequence: (binary_expression left: (identifier) right: (decimal_integer_literal)) alternative: (binary_expression left: (parenthesized_expression (binary_expression left: (identifier) right: (decimal_integer_literal))) right: (decimal_integer_literal))))))))) (expression_statement (method_invocation object: (field_access object: (identifier) field: (identifier)) name: (identifier) arguments: (argument_list (identifier))))))