task 0 q3

#Q3 simple logic of palindrome sequences

from string import ascii_lowercase as abcd
n=int(input())
str=input()
str1=[i for i in str.split()]

a=97
x = 0
y=True
for x in range(n//2):
    if str1[x]==str1[n-x-1]:
         pass
    else:
        print("false")
        y=False
        break
if y:
    for x in range (n//2-1):
        if str1[x+1]==str1[x] or str1[x+1]==chr(ord(str1[x])+1):
            pass
        else:
            print ("false")
            y=False

if y:
    print("true")