#include<bits/stdc++.h>
using namespace std;
int main(){
	int n=0;
	long long a=1,b=1;//1，2两项 
	float c=0;
	cin>>n;
	switch(n){
	case 1: cout<<"1.00";break; 
	case 0: cout<<"0.00";break;
	default :
	{
		for(int i=3;i<=n;i++){
		c=a+b;
		a=b;
		b=c;}		
	cout<<fixed<<setprecision(2)<<c;}}
	
	return 0;
}*