ln = int(input())
s = input()[:ln]
rs = s[::-1]


def cycle(s):
    return s[1:] + s[0]


cs = cycle(s)
if s == rs:
    print(0)
else:
    r = 1
    while True:
        if cs == s:
            r = -1;
            break
        if cs == rs:
            break
        r += 1
        cs = cycle(cs)
    print(r)