//#include<iostream>
#include<cstdio>

char a[210],b[210];
FILE*f=fopen("nunta.in","r");
FILE*g=fopen("nunta.out","w");

short n,aux,nra,nrb,i,j,p,t;
int main()
{



    fscanf(f,"%hd",&n);
    if(n<=2)
        fprintf(g,"%hd",n);
    else
    {

        a[0]=1;
        b[0]=2;
        nra=nrb=0;
        for(j=3; j<=n; j++)
        {


         //   short aux,t=0,p;
            t=0;
            for(i=0; i<=nra||i<=nrb||t!=0; i++)
            {

                aux=a[i];
                a[i]=b[i];
                p=aux+t+b[i];
                b[i]=(aux+t+b[i])%10;
                t=p/10;

            }
            nra=nrb;
            nrb=i-1;
        }
        for(i=nrb; i>=0; i--)
            fprintf(g,"%c",b[i]+'0');
    }
    return 0;
}