CF500A New Year Transportation

New Year is coming in Line World! In this world, there are $ n $ cells numbered by integers from $ 1 $ to $ n $ , as a $ 1×n $ board. People live in cells. However, it was hard to move between distinct cells, because of the difficulty of escaping the cell. People wanted to meet people who live in other cells. So, user tncks0121 has made a transportation system to move between these cells, to celebrate the New Year. First, he thought of $ n-1 $ positive integers $ a_{1},a_{2},...,a_{n-1} $ . For every integer $ i $ where $ 1

The first line contains two space-separated integers $ n $ ( $ 3

If I can go to cell $ t $ using the transportation system, print "YES". Otherwise, print "NO".

In the first sample, the visited cells are: $ 1,2,4 $ ; so we can successfully visit the cell $ 4 $ . In the second sample, the possible cells to visit are: $ 1,2,4,6,7,8 $ ; so we can't visit the cell $ 5 $ , which we want to visit.