def reverse(s):
    for i in range(len(s)//2):
        if s[i]!=s[len(s)-i-1]:
            return False
    return True



n=int(input())
s = input()

a=s[-1]

for i in range(n):
    if s[i] == a:
        s1=s[i:]
        if reverse(s1):
            print(i, end = '')
            break