#include<bits/stdc++.h> using namespace std; const int N=1e4+100; int n,a[N],f; int main() { cin>>n; for(int i=1;i<=n;i++) { cin>>a[i]; } cin>>f; int l=0,r=n; while(l<r) { int mid=l+(r-l)/2+1; if(a[mid]<f) { l=mid; } else if(a[mid]>f) { r=mid-1; } else if(a[mid]==f) { cout<<mid; return 0; } } cout<<-1; return 0; }