A. Polo the Penguin and Stringstime limit per test2 secondsmemory limit per test256 megabytesinputstandard inputoutputstandard outputLittle 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:  The string consists of n lowercase English letters (that is, the string's length equals n), exactly k of these letters are distinct.  No two neighbouring letters of a string coincide; that is, if we represent a string as s = s1s2... sn, then the following inequality holds, si ≠ si + 1(1 ≤ i < n).  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... xp is lexicographically less than string y = y1y2... yq, if either p < q and x1 = y1, x2 = y2, ... , xp = yp, or there is such number r (r < p, r < q), that x1 = y1, x2 = y2, ... , xr = yr and xr + 1 < yr + 1. The characters of the strings are compared by their ASCII codes.InputA 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.OutputIn a single line print the required string. If there isn't such string, print "-1" (without the quotes).ExamplesInput7 4OutputababacdInput4 7Output-1
Input7 4
Outputababacd
['greedy', '*1300']