#include<fstream.h>
int i,j,n,s1[1000],s2[1000],s3[1000];
int sum(int m){
	int t=0,i;
	for(i=1;i<=m+1;i++){
		s3[i]=s1[i]+s2[i]+t;;
		t=s3[i]/10;
		s3[i]%=10;
	}
	for(i=1;i<=s2[0]+1;i++){
		s1[i]=s2[i];
		s2[i]=s3[i];
	}
	s1[0]=s2[0];
	if(s3[s2[0]+1])
		s2[0]++;
	return 0;
}
int main(){
   ifstream fin("nunta.in");
   ofstream fout("nunta.out");
	fin>>n;
	s1[0]=1;
	s2[0]=1;
	s1[1]=1;
	s2[1]=2;
	if(n==1)
	  fout<<"1";
	else if(n==2)
	  fout<<"2";
	else{for(i=3;i<=n;i++)
		sum(s2[0]);
	for(i=s2[0];i>=1;i--)
      fout<<s2[i];      }
   fin.close();
   fout.close();
   return 0;
}