import sys

# sys.setrecursionlimit(200005)
# sys.set_int_max_str_digits(200005)
int1 = lambda x: int(x)-1
pDB = lambda *x: print(*x, end="\n", file=sys.stderr)
p2D = lambda x: print(*x, sep="\n", end="\n\n", file=sys.stderr)
def II(): return int(sys.stdin.readline())
def LI(): return list(map(int, sys.stdin.readline().split()))
def LLI(rows_number): return [LI() for _ in range(rows_number)]
def LI1(): return list(map(int1, sys.stdin.readline().split()))
def LLI1(rows_number): return [LI1() for _ in range(rows_number)]
def SI(): return sys.stdin.readline().rstrip()

dij = [(0, 1), (-1, 0), (0, -1), (1, 0)]
# dij = [(0, 1), (-1, 0), (0, -1), (1, 0), (1, 1), (1, -1), (-1, 1), (-1, -1)]
# inf = -1-(-1 << 31)
inf = -1-(-1 << 62)

md = 10**9+7
# md = 998244353

def s(a,b,c,d,e,f):
    a-=e
    c-=e
    b-=f
    d-=f
    return abs(a*d-b*c)

ans=0
pp=LI()
for da,db in dij:
    a=pp[0]+da
    b=pp[1]+db
    for dc,dd in dij:
        c=pp[2]+dc
        d=pp[3]+dd
        for de,df in dij:
            e = pp[4]+de
            f = pp[5]+df
            ans=max(ans,s(a,b,c,d,e,f))

print(ans/2)