def pal(s):
    if len(s)<2:
        return True
    if s[0]!=s[-1]:
        return False
    else:
        return pal(s[1:-1])

def first(s,n):
    f = s.find(s[-1])
    if f==len(s)-1:
        return len(s)-1
    x = s[f:]
    if pal(x):
        return n-len(x)
    return first(x[1:],n)
n = int(input())
print(first(input(),n),end='')