#include <iostream>
#include <algorithm>
#include <cmath>
#include <cstring>
#include <iomanip>
#define ll long long
using namespace std;
//cout<<"Thank god, I'm alive\n";
string f[5005]={"0","1","2"};
//1 2 3 5
string add(string a,string b)
{
	int len1=a.size();
	int len2=b.size();
	int num1[1005]={0};
	int num2[1005]={0};
	int ans[10005]={0};
	string final="";
	for(int i=0;i<len1;i++)
	{
		num1[i]=a[len1-1-i]-'0';
	}
	for(int i=0;i<len2;i++)
	{
		num2[i]=b[len2-1-i]-'0';
	}
	for(int i=0;i<max(len1,len2);i++)
	{
		ans[i]=num1[i]+num2[i];
	}
	ll high=0;
	for(int i=0;i<=max(len1,len2);i++)
	{
		ans[i+1]+=ans[i]/10;
		ans[i]%=10;
		if(ans[i]!=0)
		{
			high=i;
		}
	}
	for(int i=0;i<=high;i++)
	{
		final=char(ans[i]+48)+final;
	}
	return final;
}
int main()
{
	int n;
	cin>>n;
	for(int i=3;i<=n;i++)
	{
		f[i]=add(f[i-1],f[i-2]);
	}
	cout<<f[n];
	return 0;
}