#include<iostream>
#include<cstdio>
using namespace std;
int main()
{
    int a,b,n;
    float s;
    a=0;b=0;s=1;
    cin>>n;
    for(int i=1;i<=n-1;i++)
    {
        a=b;b=s;
		s=a+b;
    }
	printf("%.2f",s);
}