#include <iostream>

using namespace std;

class myrunge
{
   public:
   virtual double fk(double x) = 0;
};

class RungeKutta : public myrunge
{

      public:
      void step(double *pt, double *px, double h);
      double fk(double x);
      double a;
};

double RungeKutta::fk(double x)
{
   return  (a*x);
}

void RungeKutta::step(double *pt, double *px, double h)
{
   double f;
   *px = 1 + h * fk(1);
   *px = 1 + (h / 2) * ( fk(1) + fk(*px));
    f = fk(*pt);
   *pt = *pt + 0.1;
}

int main()
{
  
  return 0;
}