import java.math.BigInteger;
import java.util.*;

public class Main
{
    public static void main(String args[])
    {
        Scanner sourse = new Scanner(System.in);    
        while(sourse.hasNext())
        {
            int n = sourse.nextInt();
            BigInteger ans = BigInteger.ONE;
            BigInteger ans1= BigInteger.ONE;
            BigInteger ans2 = null;
            for(int i=2;i<=n;i++)
            {
                ans2=ans.add(ans1);
                ans=ans1;
                ans1=ans2;
            }
            if(n==1)
            System.out.println(ans);
            else if(n==0)
            System.out.println('\n');
            else
            System.out.println(ans2);
        }
        sourse.close();
    }
}