find the missing number program

import java.util.*;

public class Main {
    public static void main(String[] args) {
    int a[]={1,2,3,4,6,7};
    int n=a.length+1;
    int sum=0;
    int sum1=n*(n+1)/2;
    for(int i=0;i<a.length;i++){
      sum=sum+a[i];
    }
    System.out.println(sum1-sum);
  }
}