#include<math.h>
#include<iostream>
#include<fstream>

using namespace std;

int
main()
{
  double t, dt;
  double ts, y0, p0;
  int nsteps;
  string filename;

  cout << "Input initial position (y0):" << endl;
  cin >> y0;
  cout << "Input initial momentum:" << endl;
  cin >> p0;
  cout << "Input step (dt):" << endl;
  cin >> dt;
//  cout << "Input number of steps:" << endl;
//  cin >> nsteps;
//  Alternatively:
  double tmax;
  cout << "Maximum time (tmax):" << endl;
  cin >> tmax;
  nsteps = int(tmax/dt);
  cout << "Input File name: "<< endl;
  cin >> filename;
////////////////////////////////////////////////////  

  double p = p0, y = y0;
  double pi = acos(-1.);
  double w = -4.*pi*pi;
  double ek, ep;

  ofstream fout;
  fout.open(filename.c_str());
  if(!fout) {
     cout << "Error: Unable to open file" << endl;
     exit(-1);
  }

  for(int n = 1; n <= nsteps; n++){
    y += p*dt; 
    p += w*y*dt; 
    ek = 0.5*p*p;
    ep = 2*pi*pi*y*y;
    fout << n*dt << " " << y << " " << p << " " << ek << " " << ep << " " << ek+ep << endl;
  }

  fout.close();
  return 0;
}