using static System.Console;
using static System.Math;
class E { static void Main() { new J(); } }
class J
{
	public J()
	{
		var x = decimal.Parse(ReadLine());
		WriteLine("{0:f30}", F(x));
	}
	decimal F(decimal x)
	{
		var s = 0m;
		while (x >= 1) { s -= 1 / (x * x); x--; }
		var c = new decimal[] {
			0.934802200544679309417245499938m, -0.828796644234319995596334261160m,
			0.704545517001218618220166344353m, -0.579041637777870865089320320672m,
			0.463064525101479010073147884140m, -0.362149365025194051925732985545m,
			0.278080813330645790953150737945m, -0.210309873024092540182120622101m,
			0.157053201821111699102843595237m, -0.116040726325439516635723316840m,
			0.0849687937610356121486220604335m, -0.0617403601848552125315158487211m,
			0.0445665566678958306556779466182m, -0.0319863470099671709328335162947m,
			0.0228430551900062099110866340887m, -0.0162421055545558554090252415968m,
			0.0115040422365013313712234041955m, -0.00812016943046959528636976736546m,
			0.00571405369517650261958028746006m, -0.00400980350070223863383270061075m,
			0.00280683779121192659670361349559m, -0.00196032082598494370720627822094m,
			0.00136627989340513565859899322380m, -0.000950453775778187902602080505409m,
			0.000660036593451655151214331603647m, -0.000457625059139312543832780856133m,
			0.000316817218910202975530282277437m, -0.000219034072844732759935058022801m,
			0.000151237789910656222955212455099m, -0.000104301914852397820298442191236m,
			0.0000718524264191639058262780448723m, -0.0000494468295099862202971767811052m,
			0.0000339946946387761628180435201757m, -0.0000233498909994332923045440869638m,
			0.0000160244348894213221089962742765m, -0.0000109881838788395471852956277851m,
			0.00000752894078723383082806955951400m, -0.00000515495044126029632563349825079m,
			0.00000352707135140330242690462657687m, -0.00000241167271761871746973984769064m,
			0.00000164797635651075260851723994579m, -0.00000112544726764436204898458979840m,
			0.000000768162420684416899557407425635m, -0.000000524017775314297050883382225887m,
			0.000000357284846790347248585058118809m, -0.000000243483006695495816041148953475m,
			0.000000165850743688652348310398405047m, -0.000000112919655276366201633473176983m,
			0.0000000768480987293351213191380458419m, -0.0000000522776181830521508734450986940m,
			0.0000000355487803644065023978151140218m, -0.0000000241638768489802165568390156209m,
			0.0000000164190445255776551840460267393m, -0.0000000111525585456707153596406861955m,
			0.00000000757272493841648313038909070149m, -0.00000000514027389759101922671384908793m,
			0.00000000348804300193644735504757154867m, -0.00000000236615782587488842717335050584m,
			0.00000000160463576697257320212655829721m, -0.00000000108788865557460463209883475313m,
			0.000000000737346755445001157356813691020m, -0.000000000499622938115734972886821035223m,
			0.000000000338454248400980326640613846856m, -0.000000000229217692038758582267292215300m,
			0.000000000155199478984575887481037931931m, -0.000000000105058108851097428009803428715m};
		return s + S(x - 0.5m, c);
	}
	decimal S(decimal x, decimal[] a)
	{
		var s = 0m;
		for (var i = a.Length - 1; i >= 0; i--) s = a[i] + x * s;
		return s;
	}
}