public static void main ( String [ ] args ) {
  FastScanner fs = new FastScanner ( ) ;
  int n = fs . nextInt ( ) ;
  int [ ] v = new int [ n ] ;
  for ( int i = 0 ;
  i < n ;
  i ++ ) {
    v [ i ] = fs . nextInt ( ) ;
  }
  boolean inc = false ;
  boolean dec = false ;
  boolean cont = false ;
  boolean ok = true ;
  for ( int i = 0 ;
  i + 1 < n ;
  i ++ ) {
    if ( v [ i ] < v [ i + 1 ] ) {
      if ( ! dec && ! cont ) {
        inc = true ;
      }
      else {
        ok = false ;
        break ;
      }
    }
    if ( v [ i ] == v [ i + 1 ] ) {
      if ( ! dec ) {
        cont = true ;
      }
      else {
        ok = false ;
        break ;
      }
    }
    if ( v [ i ] > v [ i + 1 ] ) {
      dec = true ;
    }
  }
  if ( ok ) {
    System . out . println ( "YES" ) ;
  }
  else {
    System . out . println ( "NO" ) ;
  }
}

public static void main ( String [ ] args ) { FastScanner fs = new FastScanner ( ) ; int n = fs . nextInt ( ) ; int [ ] v = new int [ n ] ; for ( int i = 0 ; i < n ; i ++ ) { v [ i ] = fs . nextInt ( ) ; } boolean inc = false ; boolean dec = false ; boolean cont = false ; boolean ok = true ; for ( int i = 0 ; i + 1 < n ; i ++ ) { if ( v [ i ] < v [ i + 1 ] ) { if ( ! dec && ! cont ) { inc = true ; } else { ok = false ; break ; } } if ( v [ i ] == v [ i + 1 ] ) { if ( ! dec ) { cont = true ; } else { ok = false ; break ; } } if ( v [ i ] > v [ i + 1 ] ) { dec = true ; } } if ( ok ) { System . out . println ( " YES " ) ; } else { System . out . println ( " NO " ) ; } }
(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)))) (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: (array_type element: (integral_type) dimensions: (dimensions)) declarator: (variable_declarator name: (identifier) value: (array_creation_expression type: (integral_type) dimensions: (dimensions_expr (identifier))))) (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 (expression_statement (assignment_expression left: (array_access array: (identifier) index: (identifier)) right: (method_invocation object: (identifier) name: (identifier) arguments: (argument_list)))))) (local_variable_declaration type: (boolean_type) declarator: (variable_declarator name: (identifier) value: (false))) (local_variable_declaration type: (boolean_type) declarator: (variable_declarator name: (identifier) value: (false))) (local_variable_declaration type: (boolean_type) declarator: (variable_declarator name: (identifier) value: (false))) (local_variable_declaration type: (boolean_type) declarator: (variable_declarator name: (identifier) value: (true))) (for_statement init: (local_variable_declaration type: (integral_type) declarator: (variable_declarator name: (identifier) value: (decimal_integer_literal))) condition: (binary_expression left: (binary_expression left: (identifier) right: (decimal_integer_literal)) right: (identifier)) update: (update_expression (identifier)) body: (block (if_statement condition: (parenthesized_expression (binary_expression left: (array_access array: (identifier) index: (identifier)) right: (array_access array: (identifier) index: (binary_expression left: (identifier) right: (decimal_integer_literal))))) consequence: (block (if_statement condition: (parenthesized_expression (binary_expression left: (unary_expression operand: (identifier)) right: (unary_expression operand: (identifier)))) consequence: (block (expression_statement (assignment_expression left: (identifier) right: (true)))) alternative: (block (expression_statement (assignment_expression left: (identifier) right: (false))) (break_statement))))) (if_statement condition: (parenthesized_expression (binary_expression left: (array_access array: (identifier) index: (identifier)) right: (array_access array: (identifier) index: (binary_expression left: (identifier) right: (decimal_integer_literal))))) consequence: (block (if_statement condition: (parenthesized_expression (unary_expression operand: (identifier))) consequence: (block (expression_statement (assignment_expression left: (identifier) right: (true)))) alternative: (block (expression_statement (assignment_expression left: (identifier) right: (false))) (break_statement))))) (if_statement condition: (parenthesized_expression (binary_expression left: (array_access array: (identifier) index: (identifier)) right: (array_access array: (identifier) index: (binary_expression left: (identifier) right: (decimal_integer_literal))))) consequence: (block (expression_statement (assignment_expression left: (identifier) right: (true))))))) (if_statement condition: (parenthesized_expression (identifier)) consequence: (block (expression_statement (method_invocation object: (field_access object: (identifier) field: (identifier)) name: (identifier) arguments: (argument_list (string_literal))))) alternative: (block (expression_statement (method_invocation object: (field_access object: (identifier) field: (identifier)) name: (identifier) arguments: (argument_list (string_literal))))))))