#include <cstdio>

char last;
int nextDistance;

bool isPalindrome(char* string, unsigned length) {
    nextDistance = -1;
    for(unsigned i = 0; i < length; ++i) {
        if(i != 0 && string[i] == last && nextDistance == -1) {
            nextDistance = i;
        }
        if(string[i] != string[length - i - 1]) {
            return false;
        }
    }

    return true;
}

int main() {
    unsigned length, i;
    char string[500000];

    scanf("%u", &length);
    scanf("%s", string);

    last = string[length - 1];

    for(i = 0; i < length - 1; ++i) {
        if(string[i] == last) {
            if(isPalindrome(string + i, length - i)) {
                printf("%u\n", i);
                return 0;
            }
            if(nextDistance != -1) {
                i += nextDistance - 1; 
            }
        }
    }

    printf("%u\n", length - 1);

    return  0;
}