문제

링크

풀이

#include <cmath>
#include <iomanip>
#include <iostream>
using namespace std;
 
void solve(void) {
  int w, h; cin >> w >> h;
  int r; cin >> r;
 
  cout << fixed << setprecision(3) << w * h - M_PI_4 * r * r;
}
 
int main(void) {
  ios::sync_with_stdio(false);
  cin.tie(nullptr);
 
  solve();
  return 0;
}