class binarySearch{
    public static void main(String[] arg)
    {
        int n=10;
        int arr[]={10,9,8,7,6,5,4,3,2,1};
        int key=10;
        int start=0;
        int end=n-1;
       
        while(start<end)
        {
             int mid=(start*end)/2;
            if(arr[mid]==key)
            {
                System.out.println("key index is " + mid);
                break;
            }
            else if(arr[mid]<key)
            {
                end=mid-1;
            }
            else if(arr[mid]>key)
            {
                start=mid+1;
            }
            if(start>end){
                System.out.println("-1");
                
            }
        }
    }
}