include

using namespace std; int a[1000005];

int search(int x, int l, int r) {

if (l == r) {
	if (a[r] != x) {
		return -1;
	}
	return r;
}
int mid = (l + r) / 2;
if (a[mid] < x) {
	return search(x, mid + 1, r);
} else {
	return search(x, l, mid);
}

}

int main() {

int n, x;
cin >> n;
for (int i = 1; i <= n; i++) {
	cin >> a[i];
}
cin >> x;
cout << search(x, 1, n);
return 0;

}