eid mubarak to all .hope this eid bring happiness to you all

From yesterday i have just noticed that when i submit any solution, it is much faster now to check code with test case.any one know any thing??

Very often i do not understand problem statement.i have solved remarkable number of problems but i do not get over this problem. even in contest it happens if i can understand the problem i could solve it coz i know the technique.need an advice

Holy Eid mubarak to all!!Hope the day will be full of food after 1 month of ramadan.(:

Suppose i want to find the kth number of a sequence.the number will consist only of 2,4,6,8.How can i find it??any technique ?? Detail.

https://online.acmicpc.org/problems

http://codeforces.me/contest/437/problem/C

for second case if i remove 3 first cost=100 then remove 4 cost=100+100=200;(3 already removed) and 2 then will cost=200+100=300 and 1 cost=300+0=300; i find 300 ,but the result is 400, am i missing something ?