#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 n,s=2,fm,fz,fm0=1,fz0=2; cin>>n; for(int k=2;k<=n;k++){ fm=fz0; fz=fm0+fz0; s+=fz/fm; fm0=fm; fz0=fz; } printf("%.4lf",s); return 0; }