A10865 | Dasha and Stairs

On her way to programming school tiger Dasha faced her first test — a huge staircase!

The steps were numbered from one to infinity. As we know, tigers are very fond of all striped things, it is possible that it has something to do with their color. So on some interval of her way she calculated two values — the number of steps with even and odd numbers.

You need to check whether there is an interval of steps from the $l$ -th to the $r$ -th $(1<=l<=r)$ , for which values that Dasha has found are correct.

In the only line you are given two integers $a$ , $b$ $(0<=a,b<=100)$ — the number of even and odd steps, accordingly.

In the only line print "YES", if the interval of steps described above exists, and "NO" otherwise.