C++ :

#include <stdio.h>
#include <math.h>

const int MAXN = 100000 + 5;
const double PI = acos(-1.0);

double xi[MAXN];
double yi[MAXN];

double sqr(double x)
{
  return x * x;
}

int main()
{
  int casc;
  scanf("%d", &casc);
  for (int casi = 1; casi <= casc; casi++) {
    int n;
    scanf("%d", &n);

    double x = 0;
    double y = 0;
    for (int i = 0; i < n; i++) {
      scanf("%lf %lf", &xi[i], &yi[i]);
      x += xi[i];
      y += yi[i];
    }

    x /= n;
    y /= n;

    double res = 0;
    for (int i = 0; i < n; i++)
      res += sqr(x - xi[i]) + sqr(y - yi[i]);

    res *= PI * 2;
    printf("%.3f\n", res);
  }
  return 0;
}