import java.util.*; public class Main {

public static int fff(int s) {
	if(s==2||s==1) {
		return 1;
	}
	else {
		return fff(s-1)+fff(s-2);
	}
	
}
public static void main(String[] args) {
	// TODO Auto-generated method stub
	Scanner sc = new Scanner(System.in);
	int n = sc.nextInt();
	int sum = fff(n);
	System.out.println(sum);
}

}