#include<iostream> using namespace std; double fz1 = 2,fz2 = 3; double fm1 = 1,fm2 = 2; double fzz,fmz; double a; double b; int main() { cin>>b; if(b == 1) { a=2.0000; } else if(b == 2) { a=3.5000; } else { a = a+3.5000; for(int n = 3; n<=b; n++) { fzz = fz1+fz2; fmz = fm1+fm2; fz1 = fz2; fz2 = fzz; fm1 = fm2; fm2 = fmz; a = a+fzz/fmz; } } printf("%.4lf",a); return 0; }