import java.util.Scanner;
import java.util.Formatter;
import java.io.IOException;
import java.io.File;
import java.math.BigInteger;
public class nunta{
	public static void main(String args[]) throws IOException{
		Scanner f = new Scanner(new File ("nunta.in"));
		Formatter g= new Formatter(new File("nunta.out"));
		BigInteger A=new BigInteger("1");
		BigInteger B=new BigInteger("1");
		BigInteger C=new BigInteger("0");
		int n,i;
		n=f.nextInt();
		for(i=2;i<=n;++i) {
			C=A.add(B);
			A=B;
			B=C;
		}
		g.format("%d",B);
		f.close();g.close();
	}
}