Submission #6485909

---

Source Code Expand

#include <iostream>
#include <vector>
#include <algorithm>
#include <math.h>
using namespace std;

int main() {
    int N;
    cin >> N;
    vector<double> R(N);
    for (int i = 0; i < N; i++)
        cin >> R[i];

    sort(R.begin(), R.end());

    double sum = 0;
    for (int i = 0; i < N; i++) {
        if (i % 2 == 0)
            sum += R[i] * R[i];
        else
            sum -= R[i] * R[i];
    }

    printf("%.9f", sum * M_PI);
    cout << endl;
    return 0;
}

Submission Info

Judge Result