// 2007アジア地区予選D : Lowest Pyramid

#include <iostream>
#include <fstream>
#include <vector>
#include <complex>

using namespace std;

typedef complex<double> P;
typedef pair<P,double> circle;
struct L { P p, q; L(P p, P q) : p(p), q(q) {} };

const double EPS = 1e-8;

double dot(P a, P b) { return real(conj(a)*b); }
double cross(P a, P b) { return imag(conj(a)*b); }

P footPerp(L l, P p) {
	return l.p + (l.q-l.p) * dot(l.q-l.p, p-l.p) / norm(l.q-l.p);
}

double lenPerp(L l, P p){
	return abs(footPerp(l, p)-p);
}

P ssCrosspoint(L a, L b){
	double A = cross(a.q-a.p, b.q-b.p);
	double B = cross(a.q-a.p, a.q-b.p);
	return b.p + B/A * (b.q-b.p);
}

bool crossCircle(circle c1, circle c2){
	double r1 = c1.second;
	double r2 = c2.second;
	double d = abs(c1.first-c2.first);
	if(d<r1||d<r2)
		return d-abs(r1-r2)>EPS;
	return r1+r2-d>-EPS;
}

vector<P> crossPoint(circle c1, circle c2){
	vector<P> res;
	double r1 = c1.second;
	double r2 = c2.second;
	double r3 = abs(c1.first-c2.first);
	double rc = (r3*r3+r1*r1-r2*r2)/(2*r3);
	double rs = sqrt(r1*r1-rc*rc);
	P dif = (c2.first-c1.first)/r3;
	res.push_back(c1.first+dif*P(rc,rs));
	if(abs(rs) > EPS) res.push_back(c1.first+dif*P(rc,-rs));
	return res;
}

int main(){
	fstream cin("D.in");
	int x1, y1, x2, y2, x3, y3;
	while(cin >> x1 >> y1 >> x2 >> y2 >> x3 >> y3, x1|y1|x2|y2|x3|y3){
		x1 += 100, y1 += 100;
		x2 += 100, y2 += 100;
		x3 += 100, y3 += 100;
		while(x1-x2>0){
			int tmp = x1; x1 = x2; x2 = x3; x3 = tmp;
			    tmp = y1; y1 = y2; y2 = y3; y3 = tmp;
		}
		P p1 = P(x1, y1), p2 = P(x2, y2), p3 = P(x3, y3);
		double res = 1e12;
		int cnt = 0;
		for(int xa=0;xa<=200;xa++){
			for(int ya=0;ya<=200;ya++){
				if(cross(p2-p1, P(xa,ya)-p1) > -EPS) break;
				double len = abs(P(xa,ya)-p2);
				int r1 = int(len+EPS);
				for(int xb=max(0,x2-r1);xb<=min(200,x2+r1);xb++){
					if(len < abs(x2-xb)) continue;
					double dsq = sqrt(len*len-(x2-xb)*(x2-xb));
					int sqt = int(dsq+EPS);
					if(abs(dsq-sqt) > EPS) continue;
					for(int sgn=-1;sgn<=1;sgn+=2){
						int yb = sgn*sqt + y2;
						if(yb < 0 || 200 < yb) continue;
						if(abs(abs(p2-P(xb,yb)) - len) > EPS || abs(P(xb,yb)-P(xa,ya)) < EPS) continue;
						if(cross(p3-p2, P(xb,yb)-p2) > -EPS) continue;
						circle ca = make_pair(p1, abs(p1-P(xa,ya)));
						circle cb = make_pair(p3, abs(p3-P(xb,yb)));

						P pt = ssCrosspoint(L(P(xa,ya), P(xa,ya)+P(0,1)*(p2-p1)), L(P(xb,yb), P(xb,yb)+P(0,1)*(p3-p2)));
						double la = lenPerp(L(p1,p2), P(xa,ya));
						double lb = lenPerp(L(p1,p2), pt);
						if(la*la-lb*lb < EPS) continue;
						if(sqrt(la*la-lb*lb) > res) continue;

						if(!crossCircle(ca, cb)) continue;
						vector<P> cp = crossPoint(ca, cb);
						for(int i=0;i<cp.size();i++){
							int xc = cp[i].real()+0.5;
							int yc = cp[i].imag()+0.5;
							if(xc < 0 || 200 < xc || yc < 0 || 200 < yc) continue;
							if(cross(p1-p3, P(xc,yc)-p3) > -EPS) continue;
							if(abs(P(xc,yc)-cp[i]) > EPS) continue;
							res = min(res, sqrt(la*la-lb*lb));
						}
					}
				}
			}
		}
		if(res < 1e10) printf("%.7lf\n", res);
		else           puts("-1");
	}
}