#include <cmath>
#include <iostream>

// Triangle
double area(double a, double b, double c) {
  double s = (a + b + c) / 2;
  return std::sqrt(s * (s - a) * (s - b) * (s - c));
}

// Rectangle
double area(double a, double b) { return a * b; }

// Circle
double area(double a) { return M_PI * a * a; }

int main() {

  double a = 3, b = 4, c = 5;

  std::cout << "Area of a triangle with sides " << a << ", " << b << " and "
            << c << ": " << area(a, b, c) << std::endl
            << "Area of rectangle with sides " << a << " and " << b << ": "
            << area(a, b) << std::endl
            << "Area of circle with radius " << a << ": " << area(a)
            << std::endl;

  return 0;
}