参考题解

#include <iostream>
#include <cmath>
using namespace std;
int main(){
	float r;
	cin >> r;
	int p = floor(r);
	int sum = 0;
	while(p>0){
		int a = floor(sqrt(r*r-p*p));
		sum += a; 
		p--;
	}
	sum *= 4;
	cout << sum << endl;
	return 0;
}