public class C {
public static void printAllFoids(int N){
      printProcess(1,N,true);
}
 public static void printProcess(int i,int N,boolean down){
//i是节点的层数，N是一共的层数，down==true 凹 down==false 凸
if(i>N){
      return;
}else {printProcess(i+1,N,true);}
      System.out.print(down ?"凹":"凸");
      printProcess(i+1,N,false);
}
public static void main (String[]args){
      int N=3;
      printAllFoids(N)；
}}