this is my programm (WA 9):
#include <iostream>
#include <cmath>
#include <iomanip>
#define PI 3.1415926535897932
using namespace std;

int answer(int n, int k);
int main()
{
    int a,r;
    cin>>a>>r;
    double d=a/2;
    double O=2*acos(d/r);
    double s=2*r*r*(O-sin(O));
    double sk=PI*r*r;
    double sq=a*a;
    if (r<=a/2) cout<<setiosflags(ios::fixed)<<setprecision(3)<<sk<<endl;
    else if (r>=a*(sqrt(2.0)/2)) cout<<setiosflags(ios::fixed)<<setprecision(3)<<sq<<endl;
    else cout<<setiosflags(ios::fixed)<<setprecision(3)<<sk-s<<endl;
}

Please help!

should be "double d = a/2.0;" in line 3 in main function