#include <bits/stdc++>
#define int double
using namespace std;
int o(int x1, int y1, int x2, int y2)
{
  return sqrt(pow(x2 - x1, 2) + pow(y2 - y1, 2));
}
bool Check(int x1, int y1, int x2, int y2, int x3, int y3)
{
  int s = abs(x1*(y2 - y3) + x2*(y3 - y1) + x3*(y1 - y2));
  return s != 0;
}
signed main()
{
  int x1, y1, x2, y2, x3, y3; cin >> x1 >> y1 >> x2 >> y2 >> x3 >> y3;
  if (Check(x1, y1, x2, y2, x3, y3))
  {
    int AB = o(x1, y1, x2, y2);
    int AC = o(x1, y1, x3, y3);
    int BC = o(x2, y2, x3, y3);
    int s = AB + AC + BC;
    cout << fixed << setprecision(2) << s;
  }
  else cout << -1;
}

#danglam228

#include <bits/stdc++.h>
using namespace std;
int x1, y1, x2, y2, x3, y3;
int main() {
	    ios_base::sync_with_stdio(false);
    cin.tie(0); cout.tie(0);
    freopen("BAI1.INP", "r", stdin);
    freopen("BAI1.OUT", "w", stdout);
    cin >> x1 >> y1 >> x2 >> y2 >> x3 >> y3;
    double a = sqrt((x2 - x1) * (x2 - x1) + (y2 - y1) * (y2 - y1)); 
    double b = sqrt((x3 - x2) * (x3 - x2) + (y3 - y2) * (y3 - y2)); 
    double c = sqrt((x3 - x1) * (x3 - x1) + (y3 - y1) * (y3 - y1)); 
    double res = 0.5 * abs(x1*(y2 - y3) + x2*(y3 - y1) + x3*(y1 - y2));
    if (res == 0) {
        cout << "0" << endl;
    } else {
        double s = a + b + c;
        cout << fixed << setprecision(2) << s << endl;
    }

    return 0;
}