# include<iostream> # include<iomanip> # include<climits>//INT_MAX; INT_MIN的头文件 using namespace std; int main(){ int fz=2,fm=1,t,n; //int t=fz;fz=fz+fm;fm=t; //sum+=fz*1.0/fm,坑 double ans=0; cin>>n; ans=fz*1.0/fm; for(int i=2;i<=n;i++){ t=fz; fz=fz+fm; fm=t; ans+=fz*1.0/fm; } cout<<fixed<<setprecision(4)<<ans<<endl; return 0; }