#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==1)
        fprintf(g,"1");
    else if(n==2)
        fprintf(g,"2");
        else if(n==3)
            fprintf(g,"3");


    else
    {

        a[0]=2;
        b[0]=3;
        nra=nrb=0;
        for(j=4; j<=n; j++)
        {


            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');
    }

}