635 B | 635 chars
import sys
from math import sqrt, pi, sin, factorial, ceil, floor
BLANK = " "
inp = input
# inp = lambda : sys.stdin.readline()[:-1].strip()
mii = lambda x = BLANK : [*map(int,inp().split(x))]
mfi = lambda x = BLANK : [*map(float,inp().split(x))]
ii = lambda : int(inp())
fi = lambda : float(inp())
p = print
def solve():
l, w = mii()
avg = w // l
left = w % l
ans = ""
for i in range(l):
z = avg
if i < left:
z += 1
if z > 26 or z <= 0:
p("impossible")
return
ans += chr(z + 96)
p(ans)
if __name__ == "__main__":
tc = 1
for t in range(1, tc+1):
ret = solve()