[Silver 3] 2193번 이친수

import java.io.*;

public class Main {
    public static void main(String[] args) throws IOException {
        BufferedReader br = new BufferedReader(new InputStreamReader(System.in));
        int n = Integer.parseInt(br.readLine());
        long[][] dp = new long[91][2];
        dp[1][1] = 1;
        dp[2][0] = 1;
        
        for(int i=3; i<=90; i++) {
            for(int j=0; j<=1; j++) {
                if(j==0) { dp[i][0] = dp[i-1][0]+dp[i-1][1]; }
                else { dp[i][1] = dp[i-1][0]; }
            }
        }
        
        System.out.println(dp[n][0]+dp[n][1]);
    }
}