from math import sqrt

def colinear(x1, y1, x2, y2, x3, y3):
	a = x1 * (y2 - y3) +  x2 * (y3 - y1) +  x3 * (y1 - y2)
	if a == 0:
		return True
	else:
		return False 



def distance(x1, x2, y1, y2):
	xd = (x1 - x2) ** 2
	yd = (y1 - y2) ** 2
	return sqrt(xd + yd)


def check(cx, cy, r, x, y, n):
	for i  in range(n):
		d = distance(cx, x[i], cy, y[i])
		if d - r > 0.01:
			return False
	return True
	


def circlebydiaendpoints(x1, y1, x2, y2):
	cx = (x1 + x2) / 2
	cy = (y1 + y2) / 2
	r = distance(cx, cy, x1, y1)
	return cx, cy, r


def makeCircumcircle(x1, y1, x2, y2, x3, y3):
	x12 = x1 - x2 
	x13 = x1 - x3
	y12 = y1 - y2 
	y13 = y1 - y3 
	y31 = y3 - y1 
	y21 = y2 - y1 
	x31 = x3 - x1 
	x21 = x2 - x1 
	sx13 = x1 ** 2 - x3 ** 2 
	sy13 = pow(y1, 2) - pow(y3, 2) 
	sx21 = pow(x2, 2) - pow(x1, 2) 
	sy21 = pow(y2, 2) - pow(y1, 2) 
	f = ((sx13) * (x12) + (sy13) * (x12) + (sx21) * (x13) + (sy21) * (x13)) / (2 * ((y31) * (x12) - (y21) * (x13))) 
	g = ((sx13) * (y12) + (sy13) * (y12) + (sx21) * (y13) + (sy21) * (y13)) / (2 * ((x31) * (y12) - (x21) * (y13))) 
	c = -pow(x1, 2) - pow(y1, 2) - 2 * g * x1 - 2 * f * y1 
	cx = -g
	cy = -f
	sqr_of_r = h * h + k * k - c
	r = sqrt(sqr_of_r)
	return cx, cy, r


def main():
	n = int(input())
	x = []
	y = []
	for _ in range(n):
		a, b = input().split(' ')
		a = int(a)
		b = int(b)
		x.append(a)
		y.append(b)
	ans = -1
	for i in range(n - 1):
		for j in range(i + 1, n):
			cx, cy, r = circlebydiaendpoints(x[i], y[i], x[j], y[j])
			if check(cx, cy, r, x, y, n):
				if ans == -1:
					ans = r
				elif ans > r:
					ans = r



	for i in range(n - 2):
		for j in range(i + 1, n - 1):
			for k in range(j + 1, n):
				if colinear(x[i], y[i], x[j], y[j], x[k], y[k]):
					continue
				else:
					cx, cy, r = makeCircumcircle(x[i], y[i], x[j], y[j], x[k], y[k])
					if check(cx, cy, r, x, y, n):
						if ans == -1:
							ans = r
						elif ans > r:
							ans = r


	print(ans)
	
	
if __name__ == "__main__":
	main()



### FIXED CODE ###

from math import sqrt

def colinear(x1, y1, x2, y2, x3, y3):
	a = x1 * (y2 - y3) +  x2 * (y3 - y1) +  x3 * (y1 - y2)
	if a == 0:
		return True
	else:
		return False 



def distance(x1, y1, x2, y2):
	xd = (x1 - x2) ** 2
	yd = (y1 - y2) ** 2
	return sqrt(xd + yd)


def check(cx, cy, r, x, y, n):
	for i  in range(n):
		d = distance(cx, cy, x[i], y[i])
		if d - r > 00.1:
			return False
	return True
	


def circlebydiaendpoints(x1, y1, x2, y2):
	cx = (x1 + x2) / 2
	cy = (y1 + y2) / 2
	r = distance(cx, cy, x1, y1)
	return cx, cy, r


def makeCircumcircle(x1, y1, x2, y2, x3, y3):

	ox = (min(min(x1, x2), x3) + max(min(x1, x2), x3)) / 2
	oy = (min(min(y1, y2), y3) + max(min(y1, y2), y3)) / 2
	ax = x1 - ox
	ay = y1 - oy
	bx = x2 - ox
	by = y2 - oy
	cx = x3 - ox
	cy = y3 - oy
	d = (ax * (by - cy) + bx * (cy - ay) + cx * (ay - by)) * 2
	x = ((ax*ax + ay*ay) * (by - cy) + (bx*bx + by*by) * (cy - ay) + (cx*cx + cy*cy) * (ay - by)) / d
	y = ((ax*ax + ay*ay) * (cx - bx) + (bx*bx + by*by) * (ax - cx) + (cx*cx + cy*cy) * (bx - ax)) / d
	cx = ox + x
	cy = oy + y
	r = max(max(distance(cx, cy, x1, y1), distance(cx, cy, x2, y2)), distance(cx, cy, x3, y3))
	return cx, cy, r


def main():
	n = int(input())
	x = []
	y = []
	for _ in range(n):
		a, b = input().split(' ')
		a = float(a)
		b = float(b)
		x.append(a)
		y.append(b)
	ans = -1
	for i in range(n - 1):
		for j in range(i + 1, n):
			cx, cy, r = circlebydiaendpoints(x[i], y[i], x[j], y[j])
			if check(cx, cy, r, x, y, n):
				if ans == -1:
					ans = r
				elif ans > r:
					ans = r



	for i in range(n - 2):
		for j in range(i + 1, n - 1):
			for k in range(j + 1, n):
				if colinear(x[i], y[i], x[j], y[j], x[k], y[k]):
					continue
				else:
					cx, cy, r = makeCircumcircle(x[i], y[i], x[j], y[j], x[k], y[k])
					if check(cx, cy, r, x, y, n):
						if ans == -1:
							ans = r
						elif ans > r:
							ans = r


	print(ans)
	
	
if __name__ == "__main__":
	main()