#include <iostream>
#include <vector>

using namespace std;

bool is_pali(vector<char>& v, int start, int end)
{
    if(start == end) return true;
    for(int i = start, j = end; i <= start + end / 2; i++, j--)
    {
        if(v[i] != v[j]) return false;
    }
    return true;
}

int main() {
    long long N;
    cin >> N;

    vector<char> v ;

    char c;
    for(int i = 0; i < N; i++)
    {
        cin >> c;
        v.push_back(c);
    }

    int w = 0;
    for(int i = 0; i < N; i++)
    {
        if(is_pali(v, i, v.size() - 1))
        {
            w = i;
            break;
        }
    }

    cout << w << endl;
    return 0;
}