#include <bits/stdc++.h>
using namespace std;

const int N = 1e6+10;

int a[N],b[N],c[N];

int main()
{
	int n,x=1;
	cin>>n;
	a[1] = 1, b[1] = 2;
	
	if(n < 3)
	{
		cout<<n;
		return 0;
	}
	for(int i = 3;i <= n; ++i)
	{
		for(int j = 1;j <= x; ++j)
		{
			c[j] = a[j] + b[j];
			c[j + 1] += c[j] / 10;
			c[j] %= 10;
		}
		if(c[x+1] > 0) x++;
		for(int w = 1;w <= x; ++w) a[w] = b[w];
		for(int w = 1;w <= x; ++w) b[w] = c[w];
	}
	
	for(int i = x; i >0; i--) cout<<b[i];
	return 0;
}