Conjecture

import java.util.Scanner;

public class Viikko4_d {

    public static void main(String[] args) {
        // TODO code application logic here

        Scanner s = new Scanner(System.in);
        int a = s.nextInt();
        
        if (a < 7) {
            System.out.println(7);
        } else if (a%3 == 2) {
            System.out.println(a+2);
        } else if (a%3 == 1 || a%3 == 0) {
            System.out.println(a+1);
        }
    }
}

Test 1

Verdict: ACCEPTED

Test 2

Verdict: ACCEPTED

Test 3

Verdict: ACCEPTED

Test 4

Verdict: ACCEPTED

Test 5

Verdict: ACCEPTED

Test 6

Verdict: ACCEPTED

Test 7

Verdict: ACCEPTED

Test 8

Verdict: ACCEPTED

Test 9

Verdict: ACCEPTED

Test 10

Verdict: ACCEPTED

Test 11

Verdict: ACCEPTED

Test 12

Verdict: ACCEPTED

Test 13

Verdict: ACCEPTED

Test 14

Verdict: ACCEPTED

Test 15

Verdict: ACCEPTED

Test 16

Verdict: ACCEPTED