#include<iostream> // cin\cout\endl #include<cstdio> //scanf()\printf() #include<cstring> // strcpy()\strcat()\strcmp()\strlen()\memset() #include<cmath> //sqrt()\pow()\abs()\ceil()\floor()\max()\min() using namespace std; int main(){ double s=2,n,fz0=2,fm0=1,fz,fm; cin>>n; for(int i=2;i<=n;i++){ fm=fz0; fz=fz0+fm0; s+=fz/fm; fm0=fm; fz0=fz; } printf("%.4lf",s); return 0; }