func_code_string: #include <bits/stdc++.h>   using namespace std;   double r[1000];   double p = atan(1.) * 4.;   int main() {     double rez = 0;     int n;     cin >> n;     for (int i = 0; i < n; i++) cin >> r[i];     sort(r, r + n);     bool t = true;     for (int i = n - 1; i >= 0; i--) {       if (t)         rez += r[i] * r[i] * p;       else         rez -= r[i] * r[i] * p;       t = !t;     }     printf( %.6f , rez);     cin >> n;     return 0;   }   