Hi, coders. I welcome you to Like Shiyan Simulation Round 2. This round will be held on OJ Essential. As usual, you can take any 1h of your spare time.

Hints:

1. Problems: 4 (100-100-50-50)

2. Time: 1h

3. Difficulty: Around Div2D

4. 1 from Atcoder,2 from LOJ,1 from Topcoder(Modified)

5. OI Rule

6. Contest Writer:XGN

# Editorial

## Problem A - The Lucky Sum

If N>17, the answer is always "YES". How to get this result?

First you need to know that if an integer N can be represented as the lucky sum, N must satisfy the only condition:

Then because gcd(4,7)=1, so the maximum number that cannot be obtained is lcm(4,7)-4-7=17

**Source/Extra** Topcoder - THELUCKYSUM

**Expected Difficulty** d2a

## Problem B - The Game

**Source** Atcoder AGC007D

**Expected Difficulty** d2c for 95%, d2e for AC

## Problem C - The Gloves

**Source** BOI 2008

**Expected Difficulty** d2c