$8.$ Write a program to complete the following task $($you need to explain your approach in words; you cannot simply write the code to get full points$)$:An array has n $-1$ elements, which are consecutive integers from n consecutive numbers with one missing $($for example, in the range $39,$ the array might be $[3,6,9,7,8,4],$ missing the number $5).$ Try to find the missing number using the fastest method possible.