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