Generous Kefa
题目描述
One day Kefa found n baloons. For convenience, we denote color of i-th baloon as si − 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.
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.
Answer to the task − «YES» or «NO» in a single line.
You can choose the case (lower or upper) for each letter arbitrary.
4 2
aabb
YES
6 3
aacaab
NO
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».
题目来源：fps-www.educg.net-codeforce-1-2833.xml.zip；FPS 共享题包，题包内第 61 题。保留原作者与原赛事署名。