#include <iostream>

using namespace std;

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

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

class RungeKutta : public myrunge
{
      public:
      void step(double *pt, double *px, double h);
      double fk(double x);
      private w;
};

void RungeKutta::step(double *pt, double *px, double h)
{
   double f;
   *px = 1 + h * fk(0,1);
   *px = 1 + (h / 2) * ( fk(0,1) + fk(*pt,*px));
    f = fk(*pt,*px);
   *pt = *pt + 0.1;
}



int main()
{
  
  return 0;
}