rt，不小心算出了近似圆周率。

#include <iostream>
#include <cmath>
using namespace std;

long long count_squares_in_circle(int R) {
    long long count = 0;
    long long R2 = (long long)R * R;

    for (int i = -R; i <= R; ++i) {
        if ((i + 0.5) * (i + 0.5) > R2) {
            continue;
        }

        int max_j = floor(sqrt(R2 - (i + 0.5) * (i + 0.5)));
        int min_j = ceil(-sqrt(R2 - (i + 0.5) * (i + 0.5)));

        if (max_j >= min_j) {
            count += (max_j - min_j + 1);
        }
    }

    return count;
}

int main() {
    int R;
    cin >> R;

    cout << count_squares_in_circle(R) << endl;

    return 0;
}