#include <iostream>
//#include <fstream>
#include <cmath>
#include <cstdlib>
using namespace std;
//#define D 0.306
double fun(double E0)
{
  double result;
  double E0_2=E0*E0;
  double a=sqrt(E0_2-1)*(E0_2*E0_2/30.-3.0*E0_2/20-2./15.);
  double a2=E0/4*log(E0+sqrt(E0_2-1));
  result=a+a2;
  return result;
}
int main()
{
  
  //ofstream fout(argv[3]);  // 出力ファイルを作成する

  //if(!fout) {
  //  cout << "Cannot open output file.\n";
  //  return 1;
  //}
// log plot
  double Qvalue=999999.0;
  cout << "input Q value(1.81):";
  cin >> Qvalue;
  double E0=(Qvalue+0.511)/0.511;
  double fermiFun=fun(E0);  
  cout << "fermiFunction: " << fermiFun << endl;        
  double tau;
  double Gf=1.166e-11;
  double M2=2.;
  tau=197.e-15*2.0*pow(3.141592,3)/(3.00e8*Gf*Gf*M2*fermiFun*pow(0.511,5));
  cout << "tau: " << tau << endl;  
  //ifstream fin(argv[1]);   // 入力ファイルを開く
  //int degree;
  //double dvalue;
  
  //while(!fin.eof()) {
  //  fin >> degree >> dvalue;
    
  //  cout << degree <<" " << dvalue*dvalue << endl;
  //}

  //fin.close();

  return 0;
}