# include<iostream>//a=96 using namespace std; int main(){ int n; cin>>n; double a=0.0,b=2.0,c=1.0,d=0.0; for(int i=1;i<=n;i++){ a=a+b/c; d=b; b=b+c; c=d; } printf("%.4lf",a); return 0; }