import java.util.*;
import java.io.*;
class Main {
public static void main(String args[]) throws Exception {
BufferedReader br = new BufferedReader(new InputStreamReader(System.in));
int input = Integer.parseInt(br.readLine());
System.out.println(fibo(input));
}
public static int fibo(int data) {
if(data == 0) {
return 0;
}else if(data == 1) {
return 1;
}
return fibo(data - 1) + fibo(data - 2);
}
}