b = int(input())
x = True
a = input()
z = a[::-1]
if a == a[::-1]:
    print(0)
else:
    for i in range(1, b):
        a = a[1:b] + a[0]
        if a == z:
            print(i)
            x = False
            break
    if x:
        print(-1)