public int FindPosition(int num, int[] arr)  
            {  
                int left = 0;  
                int right = arr.Length - 1;  
      
      
                while (left < right - 1)  
                {  
                    if (arr[left] == num)  
                    {  
                        return left;  
                    }  
                    if (arr[right] == num)  
                    {  
                        return right;  
                    }  
      
      
                    int middle = (left + right) / 2;  
                    if (num == arr[middle])  
                    {  
                        return middle;  
                    }  
                    else if (num < arr[middle])  
                    {  
                        right = middle;  
                    }  
                    else  
                    {  
                        left = middle;  
                    }  
      
      
                }  
                return -1;  
            }