#include<stdio.h>
#include<string.h>
#define lg 210
short a[lg+1],b[lg+1],c[lg+1],i,n,m;
int main()
{freopen("nunta.in","r",stdin);
 freopen("nunta.out","w",stdout);
 scanf("%d",&n);
 a[lg]=1;b[lg]=2;m=lg;
 for(;n>2;n--){
  c[lg]=b[lg]+a[lg];
  for(i=lg-1;i>=m;i--)
   c[i]=b[i]+a[i]+c[i+1]/10,c[i+1]%=10;
  if(c[m]/10) {m--;c[m]=c[m+1]/10;c[m+1]%=10;}
  memcpy(a,b,sizeof(a));
  memcpy(b,c,sizeof(a));}
 if(n==2) memcpy(a,b,sizeof(a));
 i=0;
 for(i=m;i<=lg;i++)
  printf("%d",a[i]);
 fclose(stdout);
 return 0;}