#include<stdio.h>

#define input "culori.in"
#define output "culori.out"

#define dim 257

void  citire();
int rezolva();

int n, a[dim];

FILE *in, *out;

int main()
{
	in = fopen (input, "r");
	out = fopen (output, "w");

	citire();

	rezolva();


	return 0;

}

void citire()
{
	int i;

	fscanf(in, "%d", &n);

	for(i=1; i<=(n*2)-1; i++)

		fscanf(in, "%d", &a[i]);

}

int rezolva()
{
	int i;

	for(i=1; i<n; i++)

		if(a[i]!=a[n*2-i])
		{
			fprintf(out, "0");

			return 0;
		}

	fprintf(out, "%d", n-1);

	return 0;

}