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

public class Main {
	 public static void main(String[] args) {
	      BufferedReader stdReader =new BufferedReader(new InputStreamReader(System.in));
	      try {
	    	  int N = Integer.parseInt(stdReader.readLine());
	    	  long[] dp = new long[N+1];
	    	  dp[0] = 1;
	    	  dp[1] = 1;
	    	  for(int i=2;i<N+1;i++){
	    		  dp[i] = dp[i-1] + dp[i-2];
	    	  }
	    	  System.out.println(dp[N]);
	      } catch (IOException e) {
			e.printStackTrace();
	      }
	}
}