import sys

sys.setrecursionlimit(10 ** 6)
int1 = lambda x: int(x) - 1
p2D = lambda x: print(*x, sep="\n")
def II(): return int(sys.stdin.buffer.readline())
def LI(): return list(map(int, sys.stdin.buffer.readline().split()))
def LLI(rows_number): return [LI() for _ in range(rows_number)]
def LI1(): return list(map(int1, sys.stdin.buffer.readline().split()))
def LLI1(rows_number): return [LI1() for _ in range(rows_number)]
def BI(): return sys.stdin.buffer.readline().rstrip()
def SI(): return sys.stdin.buffer.readline().rstrip().decode()
inf = 10 ** 16
md = 10 ** 9 + 7
# md = 998244353

def ev(a,b,c):
    cos=(a**2+b**2-c**2)/2/a/b
    sin=(1-cos**2)**0.5
    return a*b*sin/8

a,b,c=LI()
t=(a+b+c)/2
s=(t*(t-a)*(t-b)*(t-c))**0.5
ans=s-ev(a,b,c)-ev(b,c,a)-ev(c,a,b)
print(ans)