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