import java.io.InputStream;
import java.io.PrintWriter;
import java.lang.reflect.Array;
import java.util.ArrayList;
import java.util.Arrays;
import java.util.Collections;
import java.util.HashMap;
import java.util.HashSet;
import java.util.List;
import java.util.Map;
import java.util.Map.Entry;
import java.util.PriorityQueue;
import java.util.Scanner;
import java.util.Set;
import java.util.Stack;
import java.util.TreeMap;
import java.util.TreeSet;

import static java.util.Comparator.*;

public class Main {
    public static void main(String[] args) {
        PrintWriter out = new PrintWriter(System.out);
        Solver solver = new Solver(System.in, out);
        solver.solve();
        out.close();
    }
}
class Solver {
	Scanner sc;
	PrintWriter out;
    public Solver(InputStream in, PrintWriter out) {
    	sc = new Scanner(in);
    	this.out = out;
    }
    // ==================================================================
    long[] dp = new long[60];
    public void solve() {
    	int N = Integer.parseInt(sc.next());
    	dp[0] = 1;
    	for (int i = 0; i < N; i++) {
			dp[i+1] += dp[i];
//			out.println("dp[" + i + "] = " + dp[i] + "  -->  dp[" + (i+1) + "] = " + dp[i+1]);
			dp[i+2] += dp[i];
//			out.println("dp[" + i + "] = " + dp[i] + "  -->  dp[" + (i+2) + "] = " + dp[i+2]);
		}
    	out.println(dp[N]);
    }    
    // ==================================================================
}