iPhone - Преобразование кодировки NSString из WindowsCP1251 в UTF8

как я могу получить это преобразование из NSWindowsCP1251StringEncoding в UTF-8 ? I had several attempts but no one worked as it should. My last try was:

NSData *dt = [mystr dataUsingEncoding:NSUTF8StringEncoding];
NSString *str = [NSString alloc] initWithData:dt encoding:NSWindowsCP1251StringEncoding];

The result of str is unreadable. Did anyone encounter anything similar?