680 B | 680 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():
s = list(input())
k = ii()
l = [[] for _ in range(k)]
n = len(s)
for i in range(n):
l[i % k].append(s[i])
for i in range(k):
l[i].sort()
ans = ""
for i in range(n):
a = i % k
b = i // k
ans += l[a][b]
p(ans)
if __name__ == "__main__":
tc = 1
for t in range(1, tc+1):
ret = solve()