#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 fz=2,fm=1,s=2.0,fz0,fm0; int n; cin>>n; for(int i=2;i<=n;i++){ fz0=fz; fm0=fm; fm=fz0; fz=fm0+fz0; s=s+fz/fm; } printf("%.4lf",s); return 0; }