polycarp work new project call Polychat follow modern tendency it decide project contain chat to achieve goal Polycarp spend hour laptop implement chat server process type command include person chat Add command Remove person chat remove command send message person people currently chat include send message Send command now Polycarp wants find outgoing traffic server produce processing particular set commandspolycarp know chat server send traffic Add Remove command when Send command process server send l byte participant chat l length messageas Polycarp time ask help solve problem