#include <stdio.h>
#include <stdlib.h>
#define Nmax 1000

int interpolaciona_pretraga_rekurzivno(int a[], int l, int d, int x)
{
	if(l > d)
		return -1;

	if(x < a[l] || x > a[d])
		return -1;

	if(a[l] == a[d])
		return l;

	int s = l + (int)((double)(x - a[l])/(a[d] - a[l])*(d-l));

	if(x < a[s])
		return interpolaciona_pretraga_rekurzivno(a,l,d-1,x);
	else if(x > a[s])
		return interpolaciona_pretraga_rekurzivno(a,l+1,d,x);
	else
		return s;
}

void main()
{
	int niz[Nmax];
	int i=0, n, x;

	//printf("Unesite trazeni broj: ");
	scanf("%d", &x);

	//printf("Unesite elemente niza do EOF: ");
	while(scanf("%d", &niz[i]) != EOF)
		i++;
	n = i;

	i = interpolaciona_pretraga_rekurzivno(niz,0,n-1,x);
	printf("%d\n", i);

	exit(EXIT_SUCCESS);
}


/* ITERATIVNA VERZIJA
int interpolaciona_pretraga(int a[], int n, int x)
{
	int l,s,d;
	l = 0, d = n-1;

	while(l <= d)
	{
		if(x < a[l] || x > a[d])
			return -1;

		if(a[l] == a[d])
			return l;

		s = l + (int)((double)(x - a[l])/(a[d] - a[l])*(d-l));

		if(x < a[s])
			d = s-1;
		else if(x > a[s])
			l = s+1;
		else
			return s;
	}
	return -1;
}
*/