Pole pewnego koła

#include <iostream>
#include <math.h>
#include <iomanip>
#include <sstream>
using namespace std;
float r, d, r_2;
int main()
{
  for(int i=0; i<20; i++)
  {
  cout<<"Wej\230cie:"<<endl;
    cin >>r;
    cin>>d;
    r_2=r*r-d*d/4;
  long double pole=3.141592654*r_2;
    int pole_2=round(pole);
ostringstream ss;
ss << pole_2;
string pole_3 = ss.str();
int dlugosc=pole_3.length();
    cout<<"Wyj\230cie:"<<endl<<setprecision(dlugosc+2)<<pole<<endl;
    }
    return 0;
}
 

#include <iostream>
#include <cmath>
#include <iomanip>
#include <sstream>
using namespace std;
float r, d, r_2;
int main()
{
  for(int i=0; i<20; i++)
  {
    cin >>r;
    cin>>d;
    r_2=r*r-d*d/4;
    long double pole=3.141592654*r_2;
    int pole_2=round(pole);
    ostringstream ss;
    ss << pole_2;
    string pole_3 = ss.str();
    int dlugosc=pole_3.length();
    cout<<setprecision(dlugosc+2)<<pole<<endl;
  }
    return 0;
}

#include <iostream>
#include <cmath>
#include <iomanip>
#include <sstream>
using namespace std;
float r, d, r_2;

int main()
{
    cin >>r;
    cin>>d;
    r_2=r*r-d*d/4;
    long double pole=3.141592654*r_2;
    int pole_2=round(pole);
    ostringstream ss;
    ss << pole_2;
    string pole_3 = ss.str();
    int dlugosc=pole_3.length();
    cout<<setprecision(dlugosc+2)<<pole<<endl;
  
    return 0;
}

#include <iostream>
#include <cmath>
#include <iomanip>

using namespace std;
double r, d, P;

int main()
{
    cin >>r;
    cin>>d;
    P=(pow(r,2)-pow(d,2)/4.0)*M_PI;
	
    printf("%.2f",P);
  
    return 0;
}