#include<bits/stdc++.h>
#define bl biglong
using namespace std;
struct biglong{
	int len,p[1000];
	int &operator [] (int i){
		return p[i];
	}
};
bl operator + (bl x,bl y){
	bl a={1,{0}};
	a.len=max(x.len,y.len);
	for(int i=1;i<=a.len;i++){
		a[i]+=x[i]+y[i];
		a[i+1]+=a[i]/10;
		a[i]%=10;
	}
	if(a[a.len+1]!=0) a.len++;
	return a;
}
void input(bl &x){//还原Python输入 
	string s;
	cin>>s;
	x.len=s.size();
	for(unsigned int i=0;i<s.size();i++){
		x[s.size()-i]=s[i]-'0';
	}
	return;
}
void print(string s,bl x,string c){//还原Python输出 
	cout<<s;
	for(int i=x.len;i>=1;i--){
		cout<<x[i];
	}
	cout<<c;
}
int n;
bl a[5010]={bl{1,{0,1}},bl{1,{0,1}}};
int main() {
	cin>>n;
	for(int i=2;i<=n;i++){
		a[i]=a[i-1]+a[i-2];
	}
	print("",a[n],"");
	return 0;
}