#include <iostream>
#include <cstring>
#include <cstdlib>
#include <ctime>
using namespace std;

double value(double x)
{
  ;
  return (1. / (1. + x * x));
}


double integral(double counter, double delta)
{
  double upper;
  double lower;

  upper = value(counter);
  lower = value(counter + delta);

  return ((upper + lower) * delta / 2.);

}


double calc(int divide)
{
  double x, dx;
  double delta;
  double sum;

  sum = 0.;
  delta = 1. / divide;

  for (double counter = 0. ; counter <= 1. ; counter +=
delta) {
    sum += integral(counter, delta);
  }

  return (sum * 4.);
}


int main(int argc, char *argv[])
{
  int divide;
  double ans;
  char s[80];

  cout << "LAST_COMPILED" <<  __DATE__ <<  __TIME__ <<
'\n';
  if (argc != 2) {
    cout << "Please Input Divide Num:";
    cin >> divide;

    cout << divide << '\n';
    //cout << "Error" << '\n';
    //exit(1);
  } else{

  divide = atoi(argv[1]);
 } 
  ans = calc(divide);

  cout << "ans = " << ans << '\n';

  return 0;
}