#include <bits/stdc++.h>
using namespace std;
const int maxn = 1e6 + 5;
int n, nxt[maxn];
char s[maxn];

void cal_nxt() { 
	nxt[1] = 0;
	for (int i = 2, j = 0; i <= n; i++) {
		while (j && s[j+1] != s[i])
			j = nxt[j];
		if (s[j+1] == s[i]) j++;
		nxt[i] = j;
	}
}

int main() {
	scanf("%d%s", &n, s+1);
	cal_nxt();
	printf("%d\n", nxt[n]);
	return 0;
}