import std.conv;
import std.mathspecial;
import std.stdio;
import std.string;


const real H = 1e-6;


template sevenPointDiff(alias f){
	T sevenPointDiff(T)(T x, T h=H){
		T res;
		res = f(x + 3 * h) / 60 - 3 * f(x + 2 * h) / 20;
		res += 3 * f(x + h) / 4 - 3 * f (x - h) / 4;
		res += 3 * f(x - 2 * h) / 20 - f(x - 3 * h) / 60;
		res /= h;
		return res;
	}
}


void main(){
	auto x = readln.chomp.to!real;
	writefln("%.12f", sevenPointDiff!(digamma)(x + 1));
}