[BOJ 2193] 이친수

https://www.acmicpc.net/problem/2193

import java.io.BufferedReader;
import java.io.BufferedWriter;
import java.io.IOException;
import java.io.InputStreamReader;
import java.io.OutputStreamWriter;
import java.util.Arrays;
import java.util.StringTokenizer;

public class Main {

	public static void main(String[] args) throws IOException {
		BufferedReader br = new BufferedReader(new InputStreamReader(System.in));
		BufferedWriter bw = new BufferedWriter(new OutputStreamWriter(System.out));
		int N = Integer.parseInt(br.readLine());
		
		long[][] dp = new long[N+1][2];
		
		dp[1][0] = 0;
		dp[1][1] = 1;
		
		for (int i = 2; i <= N; i++) {
			
			dp[i][0] = dp[i-1][0]+dp[i-1][1];
			dp[i][1] = dp[i-1][0];
		}
		
		long result = dp[N][0]+dp[N][1];
		bw.write(result+"\n");		
		
		br.close();
		bw.flush();
		bw.close();
	
		
	}

}