Little penguin Polo adores strings. But most of all he adores strings of length n.

One day he wanted to find a string that meets the following conditions:

1. The string consists of n lowercase English letters (that is, the string's length equals n), exactly k of these letters are distinct.
2. No two neighbouring letters of a string coincide; that is, if we represent a string as s=s₁s₂... s_n, then the following inequality holds, s_i≠s_i+1(1≤i<n).
3. Among all strings that meet points 1 and 2, the required string is lexicographically smallest.

Help him find such string or state that such string doesn't exist.

String x=x₁x₂... x_p is lexicographically less than string y=y₁y₂... y_q, if either p<q and x₁=y₁,x₂=y₂,... ,x_p=y_p, or there is such number r (r<p,r<q), that x₁=y₁,x₂=y₂,... ,x_r=y_r and x_r+1<y_r+1. The characters of the strings are compared by their ASCII codes.

A single line contains two positive integers n and k (1≤n≤10⁶,1≤k≤26) − the string's length and the number of distinct letters.

In a single line print the required string. If there isn't such string, print "-1" (without the quotes).