C++ :

#include<iostream>
using namespace std;

float const PI = 3.14;
class circle{
public:
	circle(float r):radius(r){}
	float area(){
	    return PI * radius * radius;
	}
private:
	float radius;
};
int main(){
	float radius;
	cin>>radius;
	circle c1(radius);
	cout<<c1.area();
    return 0;
}