#include <iostream>
using namespace std;
int binary_search(int a[],int l,int r,int key){
	while(l<=r){
		int m = l+(r-l)/2;
		if(key==a[m])
			return m;
		else if(key<a[m])
			r = m-1;
		else
			l = m+1;
	}
	return -1;
}
int main(int argc, char const *argv[])
{
	int n,key;
	cout<<"Enter size of array: ";
	cin>>n;
	cout<<"Enter array elements: ";
	int a[n];
	for (int i = 0; i < n; ++i)
	{
		cin>>a[i];	
	}
	cout<<"Enter search key: ";
	cin>>key;	
	int res = binary_search(a,0,n-1,key);
	if(res != -1)
		cout<<key<<" found at index "<<res<<endl;
	else
		cout<<key<<" not found"<<endl;
	return 0;
}