#include<iostream>
#define _USE_MATH_DEFINES
#include <cmath>
int main(){
	int k;
	float cnt = 0;
	float ans;
	std::cin >> k;
	if (k == 0) {
	    ans = (M_PI * M_PI)/6;
	}
	else {
	    for (int i = 1; i <= k; i++) {
		cnt = cnt + (1./i);
	    }
	    ans = cnt/k;
	}
	
	std::cout << ans << "\n";
}