a,b,c,d,e,f = map(int,input().split())
ans = 0

l = [(1,0),(-1,0),(0,1),(0,-1)]
for aa,bb in l:
	for cc,dd in l:
		for ee,ff in l:
			x = cc + c - aa - a
			y = dd + d - bb - b
			xx = ee + e - aa - a
			yy = ff + f - bb - b
			tmp = abs(x * yy - xx * y)
			if tmp > ans:
				ans = tmp
print(ans / 2)