#include <iostream> using namespace std; int main() { int num; cin >> num; double sum = 0; const double numerator = 1.0; // 分子 for (int i = 1; i <= num; i++) { int flag = 1; double denominator = 0; // 分母 for (int j = 1; j <= i; j++) { denominator += (2 * j - 1) * flag; flag = -1 * flag; } sum += numerator / denominator; } printf("%.3lf", sum); return 0; }