#include <bits/stdc++.h>

using namespace std;

int ternary_search(int array[],int l,int r, int x)

{

if(r>=l)

{

int mid1 = l + (r-l)/3;

int mid2 = r - (r-l)/3;

if(array[mid1] == x)

return mid1;

if(array[mid2] == x)

return mid2;

if(x<array[mid1])

return ternary_search(array,l,mid1-1,x);

else if(x>array[mid2])

return ternary_search(array,mid2+1,r,x);

else

return ternary_search(array,mid1+1,mid2-1,x);

}

return -1;

}

int main() {

int size;

cin>>size;

int array[size];

for(int i=0;i<size;i++)

{

cin>>array[i];

}

int val;

cin>>val;

cout<<ternary_search(array,0,size-1,val)<<endl;

return 0;

}