1234567

#include<bits/stdc++.h>
using namespace std;
int a[105],n,l,r,mid,b;
int main(){
cin>>n;
for(int i=1;i<=n;i++)
{
cin>>a[i];
}
cin>>b;
r=n,l=1;
for(int i=1;i<=n;i++)
{
mid=(r+l)/2;
if(a[mid]>=b)r=mid+1;
else l=mid-1;
if(l>r)break;
}
if(a[mid]==b)cout<<mid;
else cout<<-1;
}