#include <stdio.h>
#include <stdlib.h>

int poredi (const void *a, const void *b) {
	return *((int*)a) - *((int*)b);
}

int main () {

	int *a = NULL, b = NULL, n,i=0,x,k;

	scanf ("%i", &n);

	while (i<n) {
		a = realloc (a, (i+1) * sizeof(int));

		if (a == NULL)
			return -1;

		scanf ("%i", &k);

		a[i] = k;

		i++;
	}

	b = a;

	scanf ("%i", &x);

	int *rez = bsearch (&x, b, n, sizeof (int), poredi);

	if (rez == NULL)
		printf ("-1\n");
	else
		printf ("%i\n", rez-b);

	free (b);
return 0;
}