def prefix(s):
    v = [0]*len(s)
    for i in range(1,len(s)):
        k = v[i-1]
        while k > 0 and s[k] != s[i]:
            k = v[k-1]
        if s[k] == s[i]:
            k = k + 1
        v[i] = k
    return v
def kmp(s,t):
    index = -1
    f = prefix(s)
    k = 0
    for i in range(len(t)):
        while k > 0 and s[k] != t[i]:
            k = f[k-1]
        if s[k] == t[i]:
            k = k + 1
        if k == len(s):
            index = i - len(s) + 1
            break
    return index
n = int(input())
s = input()
rs = s[::-1]
s = s + s
print(kmp(rs, s))