백준 1914 하노이 탑 JAVA

import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStreamReader;
import java.math.BigInteger;

public class BJ_1914 {

public static void main(String[] args) throws NumberFormatException, IOException {
    BufferedReader br = new BufferedReader (new InputStreamReader(System.in));

    int N = Integer.parseInt(br.readLine());
     BigInteger result=new BigInteger("1");    //result에 1저장 
        if(N==1) System.out.println(1);
        else {
            for(int i=0;i<N;i++) {
                result=result.multiply(new BigInteger("2"));
            }
            result=result.subtract(new BigInteger("1")); //하노이 옮기 수는 2^n-1 이기 때문에 
            System.out.println(result);
        }
        if(N<=20) {
            hanoi(N,'1','2','3');
        }


}

private static void hanoi(int N, char from, char aux, char to) {
    if(N==1) {
        System.out.println(from+" "+to);
    }else {
        hanoi(N-1,from,to,aux);
        System.out.println(from+" "+to);
        hanoi(N-1,aux,from,to);
    }



}

}