#include #include #include using namespace std; int main(){ int k; cin >> k; if(k == 0){ const double PI = acos(0.0)*2.0; cout << PI*PI/6 << endl; return 0; } double d = 0; for(int i = 1; i <= k; i++) d += 1.0/i; cout << fixed << setprecision(12) << d/k << endl; return 0; }