import fileinput
def ip(b,e):
    if(z[N+b]>=(e-b+1)/2):return 1
    return 0;
def main():
    h=0
    L=0
    R=0
    t=""
    global N
    global s
    global z
    for l in fileinput.input():
        h+=1
        if(h<2):
            N=int(l)
            continue
        t=l[:-1]
    s="".join(reversed(t))+t
    N*=2
    z=[0]*N
    for k in xrange(1,N):
        if(k<=R and z[k-L]<R-k+1):z[k]=z[k-L]
        else:
            if(k>R):R=k
            L=k
            while(R<N and s[R-L]==s[R]):R+=1
            z[k]=R-L
            R-=1
    N/=2
    for i in range(N):
        if(ip(i,N-1)==1):
            print(i)
            return
main()