#include <bits/stdc++.h>
using namespace std;
int a[5005],b[5005],c[5005],n,lc=1;
int main(){
	cin >> n;
	a[1]=1,b[1]=2;
	for (int i=3;i<=n;i++){
		memset(c,0,sizeof(c));
		for(int j=1;j<=lc;j++){
			c[j]+=a[j]+b[j];
			c[j+1]+=c[j]/10;
			c[j]%=10;
		}
		if(c[lc+1]>0) lc++;
		// c=a+b
		for (int j=1;j<=lc;j++){
			a[j]=b[j];
		}
		//a=b
		for (int j=1;j<=lc;j++){
			b[j]=c[j];
		}
      //b=a;
	}
	for (int i=lc;i>=1;i--) cout << c[i];
	return 0;
}