Write a C program to find the duplicate element in an array?

/* An array of size N contains numbers ranging from 1 to N-1.
   There is exactly one number is duplicated in the array.
   Write a C program to find the duplicated number?
*/
#include <stdio.h>
#define N 5
int main()
{
  int arr[N]; //contains integers from 1 to N-1
  int arrSum = 0; //sum of array elements
  int sum = (N * (N - 1)) / 2; //sum of 1 to N-1
  int i; //loop counter
  printf("Enter %d integers form 1 to %d, with one duplicate:", N, N-1);
  for (i = 0; i < N; i++)
  {
    scanf ("%d", &arr[i]);
    arrSum += arr[i];
  }
 
  printf("\nDuplicate number is: %d\n", arrSum - sum);
}