CF841A.Generous Kefa

One day Kefa found n baloons. For convenience, we denote color of i-th baloon as s__i — lowercase letter of the Latin alphabet. Also Kefa has k friends. Friend will be upset, If he get two baloons of the same color. Kefa want to give out all baloons to his friends. Help Kefa to find out, can he give out all his baloons, such that no one of his friens will be upset — print «YES», if he can, and «NO», otherwise. Note, that Kefa's friend will not upset, if he doesn't get baloons at all.

一天，Kefa 找到了 $n$ 个气球。为方便起见，我们将第 $i$ 个气球的颜色记作 $s_i$ —— 一个小写的拉丁字母。此外，Kefa 有 $k$ 个朋友。如果某个朋友收到了两个颜色相同的气球，他就会不高兴。Kefa 想把所有气球都分发给他的朋友们。请帮 Kefa 判断：他能否将所有气球分发完毕，使得没有任何一个朋友会不高兴？如果可以，输出 YES；否则，输出 NO。注意：如果某个朋友一个气球也没收到，他也不会不高兴。

The first line contains two integers n and k (1 ≤ n, k ≤ 100) — the number of baloons and friends.

Next line contains string s — colors of baloons.

第一行包含两个整数 $n$ 和 $k$（$1 \leq n, k \leq 100$）—— 分别表示气球的数量和朋友的数量。

下一行包含字符串 $s$ —— 气球的颜色。

Answer to the task — «YES» or «NO» in a single line.

You can choose the case (lower or upper) for each letter arbitrary.

任务的答案——单行输出「YES」或「NO」。

每个字母的大小写可任意选择。

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».

在第一个样例中，Kefa 可以将第 1 个和第 3 个气球分给第一位朋友，将第 2 个和第 4 个气球分给第二位朋友。

在第二个样例中，Kefa 需要将所有气球（颜色均为 a）分给他的所有朋友，但会剩余一个气球，因此答案为 «NO»。