#include<bits/stdc++.h> using namespace std; int n,a[114514],k; int main(){ cin>>n; int l=1,r=n; for(int i=1;i<=n;i++) cin>>a[i]; cin>>k; while(l<=r){ int mid=(l+r)/2; if(a[mid]==k){ cout<<mid; return 0; } if(k>a[mid]) l=mid+1; else r=mid-1; } cout<<-1; return 0; }