#include <iostream>
using namespace std;

int main() {
	int n, h=0, k=0;
	cin >> n;
	int A[n];
	for ( int i = 0; i < n; i++ ) {
		cin >> A[i];
	}
	for ( int i = 0; i < n; i++ ) {
		if ( A[n-1] == A[i] ) {
			int t = 1;
			for ( int j = i + 1; j < n - 1; j++ ) {
				if ( A[j] != A[ n - 1 - t ] ) {
					k++;
					break;
				}
				t++;
			}
			if ( k == 0 ) {
				h = i;
				break;
			}
			else k = 0;
		}
	}
	cout << h;
	return 0;
}