ural 1084 Goat in the Garden

 #include <cstdio>
 #include <cstring>
 #include <cmath>
 #include <algorithm>
 using namespace std;
 const double pi=acos(-1.0);

 int main()
 {
     double a,r;
     scanf("%lf%lf",&a,&r);
     if(a>=r*) printf("%.3lf\n",pi*r*r);//绳子形成的圆在正方形内
     else if(r>=sqrt()*a/) printf("%.3lf\n",a*a);//正方形在圆内
     else
     {
         double a1=a/2.0/r;
         double s1=sqrt(-a1*a1);
         double ji=atan(s1/a1);
         double s=r*s1*a/2.0*+(pi/-ji*)*r*r/2.0*;
         printf("%.3lf\n",s);
     }
     return ;
 }