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

char string[400005] = { 0 };

int ispal(char *start, char *end, int i){
    while(1){
        if((start[i]) != (*end)) return i;
        if((start + i) > end) return -1;
        i++;
        end--;
    }
}
// 14 aaabaaaaaaaaaa
int main()
{

    int n;
    scanf("%d", &n);
    scanf("%s", string);

    int len = strlen(string);
    int start = 0;
    char *end = string + len - 1;
    int i;

    for(i = 0; string[i]; i++){
        int pali = ispal(string, end, i);
        if(pali == -1){
            break;
        }
        else i = pali;
    }

    printf("%d\n", i >= len ? len - 1 : i);
    return 0;
}