[2193번] 이친수

import java.io.BufferedReader;
import java.io.FileNotFoundException;
import java.io.FileReader;
import java.io.IOException;
import java.io.InputStreamReader;
 
import java.util.StringTokenizer;
import java.util.Scanner;
 
public class Main {
    static int z=0;
    static int o=0;
    static int[] a = { 0, 0 };
 
    public static void main(String[] args) {
//        Scanner sc = new Scanner(System.in);
        FastScanner sc = new FastScanner();
        int T = sc.nextInt();
        long[] ar = new long[91];
        ar[0] = 0;
        ar[1] = 1;
        ar[2] = 1;
        ar[3] = 2;
        for(int i=4;i<=90;i++){
            ar[i] = ar[i-1]+ar[i-2];
        }
        System.out.println(ar[T]);
        
 
 
    } 
}
 
class FastScanner {
    BufferedReader br;
    StringTokenizer st;
 
    public FastScanner(String s) {
        try {
            br = new BufferedReader(new FileReader(s));
        } catch (FileNotFoundException e) {
            throw new RuntimeException(e);
        }
    }
 
    public FastScanner() {
        br = new BufferedReader(new InputStreamReader(System.in));
    }
 
    String nextToken() {
        while (st == null || !st.hasMoreElements()) {
            try {
                st = new StringTokenizer(br.readLine());
            } catch (IOException e) {
                throw new RuntimeException(e);
            }
        }
        return st.nextToken();
    }
 
    int nextInt() {
        return Integer.parseInt(nextToken());
    }
 
    long nextLong() {
        return Long.parseLong(nextToken());
    }
 
    double nextDouble() {
        return Double.parseDouble(nextToken());
    }
 
    String nextLine() {
        String str = "";
        try {
            str = br.readLine();
        } catch (IOException e) {
            e.printStackTrace();
        }
        return str;
    }
}