include

int a[1000001], m;

int find(int left, int right) {

if (left == right) {
	if (a[left] == m)
		return left;
	else
		return -1;
}
int mid = (left + right) / 2;
if (a[mid] >= m)
	return find(left, mid);
else
	return find(mid + 1, right);

}

int main() {

int n;
scanf("%d", &n);
for (int i = 1; i <= n; i++) {
	scanf("%d", &a[i]);
}
scanf("%d", &m);
printf("%d", find(1, n));
return 0;

}