https://medium.com/@arlan.abildanov26/%D1%80%D0%B5%D1%88%D0%B5%D0%BD%D0%B8%D0%B5-%D0%B7%D0%B0%D0%B4%D0%B0%D1%87%D0%B8-%D0%BF%D0%B0%D0%BD%D0%B3%D1%80%D0%B0%D0%BC%D0%BC%D0%B0-%D1%81-codeforces-520a-%D0%BD%D0%B0-%D1%81-898eab01363b