public static void main ( String [ ] args ) {
  Scanner sc = new Scanner ( System . in ) ;
  int n = sc . nextInt ( ) ;
  int m = sc . nextInt ( ) ;
  int d = sc . nextInt ( ) ;
  int [ ] arr = new int [ n * m ] ;
  boolean flag = true ;
  int count = 0 , sum = 0 ;
  for ( int i = 0 ;
  i < ( n * m ) ;
  i ++ ) {
    arr [ i ] = sc . nextInt ( ) ;
    sum += arr [ i ] ;
  }
  if ( m * n == 1 ) {
    System . out . println ( "0" ) ;
    return ;
  }
  Arrays . sort ( arr ) ;
  int cmp = arr [ ( m * n ) / 2 ] ;
  for ( int i = 0 ;
  i < ( m * n ) ;
  i ++ ) {
    if ( ( cmp - arr [ i ] ) % d == 0 ) {
      count += Math . abs ( cmp - arr [ i ] ) / d ;
    }
    else {
      flag = false ;
      break ;
    }
  }
  if ( flag == false ) System . out . println ( "-1" ) ;
  else System . out . println ( count ) ;
}

public static void main ( String [ ] args ) { Scanner sc = new Scanner ( System . in ) ; int n = sc . nextInt ( ) ; int m = sc . nextInt ( ) ; int d = sc . nextInt ( ) ; int [ ] arr = new int [ n * m ] ; boolean flag = true ; int count = 0 , sum = 0 ; for ( int i = 0 ; i < ( n * m ) ; i ++ ) { arr [ i ] = sc . nextInt ( ) ; sum += arr [ i ] ; } if ( m * n == 1 ) { System . out . println ( "0" ) ; return ; } Arrays . sort ( arr ) ; int cmp = arr [ ( m * n ) / 2 ] ; for ( int i = 0 ; i < ( m * n ) ; i ++ ) { if ( ( cmp - arr [ i ] ) % d == 0 ) { count += Math . abs ( cmp - arr [ i ] ) / d ; } else { flag = false ; break ; } } if ( flag == false ) System . out . println ( " - 1" ) ; else System . out . println ( count ) ; }
(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 (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: (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: (array_type element: (integral_type) dimensions: (dimensions)) declarator: (variable_declarator name: (identifier) value: (array_creation_expression type: (integral_type) dimensions: (dimensions_expr (binary_expression left: (identifier) right: (identifier)))))) (local_variable_declaration type: (boolean_type) declarator: (variable_declarator name: (identifier) value: (true))) (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: (parenthesized_expression (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)))) (expression_statement (assignment_expression left: (identifier) right: (array_access array: (identifier) index: (identifier)))))) (if_statement condition: (parenthesized_expression (binary_expression left: (binary_expression left: (identifier) right: (identifier)) right: (decimal_integer_literal))) consequence: (block (expression_statement (method_invocation object: (field_access object: (identifier) field: (identifier)) name: (identifier) arguments: (argument_list (string_literal)))) (return_statement))) (expression_statement (method_invocation object: (identifier) name: (identifier) arguments: (argument_list (identifier)))) (local_variable_declaration type: (integral_type) declarator: (variable_declarator name: (identifier) value: (array_access array: (identifier) index: (binary_expression left: (parenthesized_expression (binary_expression left: (identifier) right: (identifier))) right: (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: (parenthesized_expression (binary_expression left: (identifier) right: (identifier)))) update: (update_expression (identifier)) body: (block (if_statement condition: (parenthesized_expression (binary_expression left: (binary_expression left: (parenthesized_expression (binary_expression left: (identifier) right: (array_access array: (identifier) index: (identifier)))) right: (identifier)) right: (decimal_integer_literal))) consequence: (block (expression_statement (assignment_expression left: (identifier) right: (binary_expression left: (method_invocation object: (identifier) name: (identifier) arguments: (argument_list (binary_expression left: (identifier) right: (array_access array: (identifier) index: (identifier))))) right: (identifier))))) alternative: (block (expression_statement (assignment_expression left: (identifier) right: (false))) (break_statement))))) (if_statement condition: (parenthesized_expression (binary_expression left: (identifier) right: (false))) 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 (identifier)))))))