#include<cstdio>
int nr[31],nr2[31],n,i,j,k,l,nr3[31];
void pun()
    {
    for(int i=0;i<=nr[0];i++)
        nr3[i]=nr[i];
    }
void schimb()
    {
    for(int i=0;i<=nr3[0];i++)
        nr2[i]=nr3[i];
    }
void adun()
    {
    int r=0;
    for(int i=1;i<=nr[0];i++)
        {
        nr[i]=nr[i]+nr2[i]+r;
        r=nr[i]/10;
        nr[i]%=10;
        }
    if(r!=0)
        nr[++nr[0]]=r;
    }
int main ()
{
freopen("nunta.in","r",stdin);
freopen("nunta.out","w",stdout);
scanf("%d",&n);
nr[0]=1;
nr[1]=2;
nr2[0]=1;
nr2[1]=1;
for(i=3;i<=n;i++)
    {
    pun();
    adun();
    schimb();
    }
for(i=nr[0];i>=1;i--)
    printf("%d",nr[i]);
return 0;
}