https://s0.wp.com/latex.php?latex=%7B%5Cleq%5Cmax%5C%7BC_0%2C%28k%2F2%5En%2B%5Csum%5Climits_%7Bl%3D1%7D%5En+1%2F2%5El%29C_0%5C%7D%5Cleq++%281%2Bk%2F2%5En%29C_0%7D&bg=ffffff&fg=000000&s=0