#include <cstdio>

const double PI = 3.1415926535897932384626433832;

int main()
{
	const int limit = 100000;

	double x;
	scanf("%lf", &x);

	double pre = 0;
	double orig_pre = 0;

	for(int i = 1; i < limit; ++i)
		pre += 1.0 / ((x + i) * (x + i));
	for(int i = 1; i < limit + x; ++i)
		orig_pre = orig_pre + 1.0 / ((double)i * i);

	double orig_total = PI / 6 * PI;
	double orig_remain = orig_total - orig_pre;

	double ans = pre + orig_remain;

	printf("%.20lf\n", ans);
	
	return 0;
}