#include <fstream>
using namespace std;
ifstream f("exemplu.in");
ofstream g("exemplu.out");
int n,i,v[251],p;
int cautarebinara(int s, int d, int c)
{
  int mij=(s+d)/2,r;
  if (s<=d)
  {
    if (v[mij]==c)
    {
      return mij;
    }
    else
    {
      if (c<v[mij])
      {
        return cautarebinara(s,mij-1,c);
      }
      else
      {
        return cautarebinara(mij+1,d,c);
      }
    }
  }
  else
  {
    return -1;
  }
};
int main ()
{
  f>>n;
  for (i=1;i<=n;i++)
  {
    f>>v[i];
  }
  f>>p;
  g<<cautarebinara(1,n,p);
}