#include<bits/stdc++.h>

typedef long long ll;

using namespace std;

int n, d[1000001], pal;

void manacher (const string& s) {
	int n = s.size ();
	
	vector <int> p[2] = {vector <int> (n + 1), vector <int> (n)};
	
	for (int z = 0; z < 2; z++)
		for (int i = 0, l = 0, r = 0; i < n; i++) {
			int t = r - i + !z;
			if (i < r) p[z][i] = min (t, p[z][l+t]);
			int L = i - p[z][i], R = i + p[z][i] - !z;
			
			while (L >= 1 && R + 1 < n && s[L - 1] == s[R + 1]) {
				p[z][i]++;
				L--;
				R++;
			}
			
			if (R == (int) s.size () - 1) {
				pal = max (pal, R - L + 1);
			}
			
			if (R > r) l = L, r = R;
		}
}

int main () {
	
	cin >> n;
	string s;
	cin >> s;
	
		
	manacher (s);
	
	cout << n - pal;
}