Java program to find one missing number in an array of 1 to N

You are given an integer array containing 1 to n but one of the number from 1 to n in the array is missing. You need to provide optimum solution to find the missing number. Number can not be repeated in the array. 

For Example 

int[] arr1 = {1, 5, 4, 2}; 3 is missing
int[] arr1 = {7, 5, 4, 1, 2, 3}; 6 is missing

package com.seleniumtest;

public class MissingNumber 
{
    public void findMissingNumber(int[] inputArray)
    {
        //Increment by 1, total number will be one more than array size because 1 number is missing in array
        int n = inputArray.length + 1;
        int sum = n * (n+1) / 2;
        int restSum = 0;
		
        for(int i = 0; i < inputArray.length; i++)
        {
            restSum += inputArray[i];
        }
		
        int missingNumber = sum - restSum;
        System.out.println("Missing Number is:" +missingNumber);
	}

	public static void main(String args[])
	{
		int[] arr = {7, 5, 4, 1, 2, 3};
		
		MissingNumber mn = new MissingNumber();
		mn.findMissingNumber(arr);
	}
}