古典算法问题

古典问题：有一对兔子，从出生后第3个月起每个月都生一对兔子，小兔子长到第三个月
后每个月又生一对兔子，假如兔子都不死，问每个月的兔子总数为多少?

public class num6 {public static void main(String[] args) {int j, mon1, mon2;mon1 = mon2 = 1;Scanner sc = new Scanner(System.in);j = sc.nextInt();for (int i = 2; i <j; i=i+2) {mon1 = mon1 + mon2;mon2 =mon1 + mon2;}System.out.println(mon1);}}