CF841A Generous Kefa

读入一个字符串（都是小写字母），让你求出里边最多的一种字母的个数是否小于等于 $k$。，若大于输出"NO",否则输出"YES"。 第二行为一个字符串。

The first line contains two integers $ n $ and $ k $ ( $ 1

Answer to the task — «YES» or «NO» in a single line. You can choose the case (lower or upper) for each letter arbitrary.

In the first sample Kefa can give $ 1 $ -st and $ 3 $ -rd baloon to the first friend, and $ 2 $ -nd and $ 4 $ -th to the second. In the second sample Kefa needs to give to all his friends baloons of color a, but one baloon will stay, thats why answer is «NO».