📅  最后修改于: 2022-03-11 14:44:56.019000             🧑  作者: Mango
#include
#include
using namespace std;
int main(){
double R,A;
cin >> R;
A = 3.14159 * R * R;
cout << "A=" << fixed << setprecision(4) << A << endl;
return 0;
}