#include <iostream> #include <vector> using namespace std; int main() { double sum = 0; int fz1 = 2,fm1 = 1; int fz2 = 3,fm2 = 2; int n; cin>>n; if (n == 1) { sum += 2.0/1; printf("%.4lf",sum); }else if (n == 2) { sum += 2.0 / 1 + 3.0 / 2; printf("%.4lf",sum); }else { int fz,fm; sum += 2.0 / 1 + 3.0 / 2; for (int i = 3;i <= n;i++) { fz = fz1 + fz2; fm = fm1 + fm2; sum += fz * 1.0 / fm; //fz1:2 3 5 8 13 //fm2:1 2 3 5 8 //2 3 5 8 13 //fz1 fz2 fz //2 3 5 8 13 // fz1 fz2 fz fz1 = fz2; fz2 = fz; fm1 = fm2; fm2 = fm; } printf("%.4lf",sum); } return 0; }