Little Santa is hungry after doing so much hard work. He decided to cook some food for himself. He has $26$ ingredients denoted by lowercase English letters. He placed some of the ingredients in a sequence S of length N (some ingredients can occur more than once). He will select any two numbers $(L, R)$ $(1 \le L \le R \le N)$ and use all the ingredients from L to R $(S_L, S_{L+1}, ... , S_R)$ to make one dish. For different values of $(L, R)$, he can make different dishes. Two dishes are different if for two values of $(L, R)$, $(L_1, R_1)$ and $(L_2, R_2)$, $(S_{L_1}, S_{L_1+1}, ... , S_{R_1})$ is not equal to $(S_{L_2}, S_{L_2+1}, ... , S_{R_2})$.

Note: $(S_{L_1}, S_{L_1+1}, ... , S_{R_1})$ is not equal to $(S_{L_2}, S_{L_2+1}, ... , S_{R_2})$ if either $R_1 - L_1 \neq R_2 - L_2$ or there exists an integer x $(0 \le x \le (R_1 - L_1))$ such that $S_{L_1 + x} \neq S_{L_2 + x}$

Little Santa wants to make exactly K dishes with those ingredients. He tried different sequence of length N but he is not able to get exactly K dishes. He asked you to help him. Given an integer N, you have to find a sequence of the length N such that for all possible values of $(L, R)$ Little Santa can make exactly K different dishes. Sequence should only contain lowercase English letters.

Input format:
First line contains two space separated integers, N $(1 \le N \le 10^3)$ and K $(N \le K \le N+1)$.

Output format:
Print a string denoting the sequence of ingredients. Print No if there is no such sequence.