import math
a = float(input())
b = float(input())
c = float(input())
p = (a + b + c) / 2
S = math.sqrt(p * (p - a) * (p - b) * (p - c))
print(S)
aW1wb3J0IG1hdGgKCmEgPSBmbG9hdChpbnB1dCgpKQpiID0gZmxvYXQoaW5wdXQoKSkKYyA9IGZsb2F0KGlucHV0KCkpCgpwID0gKGEgKyBiICsgYykgLyAyClMgPSBtYXRoLnNxcnQocCAqIChwIC0gYSkgKiAocCAtIGIpICogKHAgLSBjKSkKCnByaW50KFMpCg==