#include<bits/stdc++.h> using namespace std; int n,a[100010],x,ans=-1; int main(){ cin>>n; for(int i=1;i<=n;i++){ cin>>a[i]; } cin>>x; int l=1,r=n; while(r>=l){ if(r==l+1){ if(a[l]==x) ans=l; if(a[r]==x) ans=r; break; } int mid=(l+r)/2; if(a[mid]==x){ ans=mid; break; } if(a[mid]>x) r=mid-1; if(a[mid]<x) l=mid+1; } cout<<ans; return 0; }