Find Duplicate in Range 0 and n-1

#include <stdio.h>

int find_duplicate(int arr[], int n) {
    int i = 0;
    while (i < n) {
        int k = i + 1;
        while (k < n) {
            if (arr[k] == arr[i]) {
                return arr[k];
            }
            k++;
        }
        i++;
    }
}

int main() {
    int n;
    scanf("%d", &n);

    int arr[100];
    for (int i = 0; i < n; i++) scanf("%d", &arr[i]);

    int result = find_duplicate(arr, n);
    printf("%d", result);
    return 0;
}