#include <stdio.h>
#include <stdlib.h>

int is_pal(char *a, char *b) {
	for (; a < b; a++, b--) {
		if (*a != *b) return 0;
	}
	return 1;
}

int main(void) {
	int n = 0;
	scanf("%d", &n);
	getchar();

	char *arr = malloc(n);

	for (int i = 0; i < n; i++) {
		arr[i] = getchar();
	}

	for (int i = 0; i < n; i++) {
		if (is_pal(arr + i, arr + n - 1)) {
			printf("%d\n", i);
			break;
		}
	}

	return 0;
}