n = int(input())
k = 1
while k * k < n:
k += 1
s = input()
a = []
for i in range(k):
a.append(s[i * k: (i + 1) * k])
res = ""
for x in range(2 * k - 1):
for i in range(0, k):
j = x - i
if j >= 0 and j < k:
res += a[i][j]
print(res)
