func_code_string: #include <bits/stdc++.h>   using namespace std;   const int MAX = 1e5 + 55;   int x[MAX];   int main() {     int n;     cin >> n;     double sum = 0;     int a[n + 1];     for (int i = 0; i < n; i++) cin >> a[i];     sort(a, a + n, greater<int>());     for (int i = 0; i < n; i++) {       if (i % 2 == 0)         sum += a[i] * a[i];       else         sum -= a[i] * a[i];     }     cout << setprecision(11) << fixed << sum * 3.1415926536;     return 0;   }   