n = int(input())
a = input()
rev_a = a[::-1]
flag = False
count = 0
for j in range(n):
    temp_a = a
    temp_a += a[:j]
    temp_a = temp_a[j:]
    count+=1
    if temp_a == rev_a:
        flag = True
        break
if not(flag):
    print(-1)
else:
    print(count-1)