#include <bits/stdc++.h>
int findDuplicate(vector<int> &arr, int n){	// Write your code here.	sort(arr.begin(), arr.end());	int start = 0;	int end = n - 1;
	while(start<=end){		int mid = start + (end - start) / 2;		if(arr[mid] == arr[mid - 1] || arr[mid] == arr[mid + 1]){			// int x = arr[mid];			return arr[mid];		}		else if(arr[mid] > mid){			start = mid + 1;		}		else{			end = mid - 1;		}	}	return -1;}