public static void main ( String [ ] args ) {
  @ SuppressWarnings ( "resource" ) Scanner scan = new Scanner ( System . in ) ;
  int N = scan . nextInt ( ) ;
  String S = scan . next ( ) ;
  int x = 0 ;
  int max = 0 ;
  for ( char s : S . toCharArray ( ) ) {
    switch ( s ) {
      case 'I' : x ++ ;
      if ( max < x ) {
        max = x ;
      }
      break ;
      case 'D' : x -- ;
    }
  }
  System . out . println ( max ) ;
}

public static void main ( String [ ] args ) { @ SuppressWarnings ( " resource " ) Scanner scan = new Scanner ( System . in ) ; int N = scan . nextInt ( ) ; String S = scan . next ( ) ; int x = 0 ; int max = 0 ; for ( char s : S . toCharArray ( ) ) { switch ( s ) { case ' I ' : x ++ ; if ( max < x ) { max = x ; } break ; case ' D ' : x -- ; } } System . out . println ( max ) ; }
(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 (modifiers (annotation name: (identifier) arguments: (annotation_argument_list (string_literal)))) 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: (integral_type) 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))) (local_variable_declaration type: (integral_type) declarator: (variable_declarator name: (identifier) value: (decimal_integer_literal))) (enhanced_for_statement type: (integral_type) name: (identifier) value: (method_invocation object: (identifier) name: (identifier) arguments: (argument_list)) body: (block (switch_expression condition: (parenthesized_expression (identifier)) body: (switch_block (switch_block_statement_group (switch_label (character_literal)) (expression_statement (update_expression (identifier))) (if_statement condition: (parenthesized_expression (binary_expression left: (identifier) right: (identifier))) consequence: (block (expression_statement (assignment_expression left: (identifier) right: (identifier))))) (break_statement)) (switch_block_statement_group (switch_label (character_literal)) (expression_statement (update_expression (identifier)))))))) (expression_statement (method_invocation object: (field_access object: (identifier) field: (identifier)) name: (identifier) arguments: (argument_list (identifier))))))