#include<bits/stdc++.h> using namespace std; long long n,m,a[10010]; int main(){ cin>>n; for(int i=1;i<=n;i++) cin>>a[i]; cin>>m; int l=1,r=n; while(l<=r){ int mid=l+r>>1; if(a[mid]==m){ cout<<mid; return 0; } if(a[mid]>m) r=mid-1; if(a[mid]<m) l=mid+1; } cout<<"-1"; return 0; }