#include<iostream>
#include<algorithm>
using namespace std;
int binarySearch(int arr[],int start,int end,int m)
{
if(start==end && arr[start]!=m)
return -1;
if(arr[start]==m)
return start;
int mid=(start+end)/2;
if(m<=arr[mid])
return binarySearch(arr,start,mid,m);
else
return binarySearch(arr,mid+1,end,m);
}
int main()
{
int n,arr[1000]={};
cin>>n;
for(int i=0;i<n;i++)
{
cin>>arr[i];
}
sort(arr,arr+n);
int m;
cin>>m;
cout<<binarySearch(arr,0,n,m);
}
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