func_code_string: #include <bits/stdc++.h>   using namespace std;   int main() {     ios_base::sync_with_stdio(false);     long double P = 3.1415926536, a[110], n;     cin >> n;     for (int i = 0; i < n; i++) {       cin >> a[i];       a[i] *= a[i];       a[i] *= P;     }     for (int i = 0; i < n; i++)       for (int j = 0; j < n - 1; j++)         if (a[j] > a[j + 1]) swap(a[j], a[j + 1]);     long double ans = 0;     for (int i = n - 1; i >= 0; i -= 2)       if (i == 0)         ans += a[i];       else         ans += a[i] - a[i - 1];     cout << setprecision(12) << ans;     return 0;   }   