public static long solve ( long num ) {
  if ( num == 1 ) return 1 ;
  long i = ( long ) Math . sqrt ( 2 * num ) - 1 ;
  long n = 1 ;
  while ( n < num ) {
    i ++ ;
    n = i * ( i + 1 ) / 2 ;
  }
  return num - n + i ;
}

public static long solve ( long num ) { if ( num == 1 ) return 1 ; long i = ( long ) Math . sqrt ( 2 * num ) - 1 ; long n = 1 ; while ( n < num ) { i ++ ; n = i * ( i + 1 ) / 2 ; } return num - n + i ; }
(method_declaration (modifiers) type: (integral_type) name: (identifier) parameters: (formal_parameters (formal_parameter type: (integral_type) name: (identifier))) body: (block (if_statement condition: (parenthesized_expression (binary_expression left: (identifier) right: (decimal_integer_literal))) consequence: (return_statement (decimal_integer_literal))) (local_variable_declaration type: (integral_type) declarator: (variable_declarator name: (identifier) value: (binary_expression left: (cast_expression type: (integral_type) value: (method_invocation object: (identifier) name: (identifier) arguments: (argument_list (binary_expression left: (decimal_integer_literal) right: (identifier))))) right: (decimal_integer_literal)))) (local_variable_declaration type: (integral_type) declarator: (variable_declarator name: (identifier) value: (decimal_integer_literal))) (while_statement condition: (parenthesized_expression (binary_expression left: (identifier) right: (identifier))) body: (block (expression_statement (update_expression (identifier))) (expression_statement (assignment_expression left: (identifier) right: (binary_expression left: (binary_expression left: (identifier) right: (parenthesized_expression (binary_expression left: (identifier) right: (decimal_integer_literal)))) right: (decimal_integer_literal)))))) (return_statement (binary_expression left: (binary_expression left: (identifier) right: (identifier)) right: (identifier)))))