public static void main ( String [ ] args ) throws IOException {
  Reader in = new Reader ( ) ;
  int n = in . nextInt ( ) ;
  int m = in . nextInt ( ) ;
  int ans = 0 ;
  int min = Math . min ( m , n ) ;
  int max = Math . max ( m , n ) ;
  if ( min == 1 ) ans = max ;
  else if ( min == 2 ) ans = ( max / 4 ) * 4 + Math . min ( max % 4 , 2 ) * 2 ;
  else ans = ( m * n ) - ( m * n ) / 2 ;
  System . out . println ( ans ) ;
}

public static void main ( String [ ] args ) throws IOException { Reader in = new Reader ( ) ; int n = in . nextInt ( ) ; int m = in . nextInt ( ) ; int ans = 0 ; int min = Math . min ( m , n ) ; int max = Math . max ( m , n ) ; if ( min == 1 ) ans = max ; else if ( min == 2 ) ans = ( max / 4 ) * 4 + Math . min ( max % 4 , 2 ) * 2 ; else ans = ( m * n ) - ( m * n ) / 2 ; System . out . println ( ans ) ; }
(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)))) (local_variable_declaration type: (integral_type) 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: (method_invocation object: (identifier) name: (identifier) arguments: (argument_list)))) (local_variable_declaration type: (integral_type) declarator: (variable_declarator name: (identifier) value: (decimal_integer_literal))) (local_variable_declaration type: (integral_type) declarator: (variable_declarator name: (identifier) value: (method_invocation object: (identifier) name: (identifier) arguments: (argument_list (identifier) (identifier))))) (local_variable_declaration type: (integral_type) declarator: (variable_declarator name: (identifier) value: (method_invocation object: (identifier) name: (identifier) arguments: (argument_list (identifier) (identifier))))) (if_statement condition: (parenthesized_expression (binary_expression left: (identifier) right: (decimal_integer_literal))) consequence: (expression_statement (assignment_expression left: (identifier) right: (identifier))) alternative: (if_statement condition: (parenthesized_expression (binary_expression left: (identifier) right: (decimal_integer_literal))) consequence: (expression_statement (assignment_expression left: (identifier) right: (binary_expression left: (binary_expression left: (parenthesized_expression (binary_expression left: (identifier) right: (decimal_integer_literal))) right: (decimal_integer_literal)) right: (binary_expression left: (method_invocation object: (identifier) name: (identifier) arguments: (argument_list (binary_expression left: (identifier) right: (decimal_integer_literal)) (decimal_integer_literal))) right: (decimal_integer_literal))))) alternative: (expression_statement (assignment_expression left: (identifier) right: (binary_expression left: (parenthesized_expression (binary_expression left: (identifier) right: (identifier))) right: (binary_expression left: (parenthesized_expression (binary_expression left: (identifier) right: (identifier))) right: (decimal_integer_literal))))))) (expression_statement (method_invocation object: (field_access object: (identifier) field: (identifier)) name: (identifier) arguments: (argument_list (identifier))))))