Missing Number in an Array

Program -

public class missingVal{

     public static void main(String []args){
        int n = 6;
        int array[] = {2,4,6,5,1};
        int sumN = (n*(n+1))/2;
        int sum = 0;
        for(int i = 0; i<n-1; i++)
        {
            sum += array[i];
        }
        System.out.println(sumN - sum);
     }
}  

Video explanation -