ab,bc,ca = (int(i) for i in input().split())

print((ab*bc//2))
def main():

    a, b, c = (int(i) for i in input().split())

    from math import sqrt

    s = (a + b + c) / 2

    print((int(sqrt(s*(s-a)*(s-b)*(s-c)))))





if __name__ == '__main__':

    main()

ab, bc, ca = (int(i) for i in input().split())
print((ab * bc // 2))

def main():
    a, b, c = (int(i) for i in input().split())
    from math import sqrt

    s = (a + b + c) / 2
    print((int(sqrt(s * (s - a) * (s - b) * (s - c)))))


if __name__ == "__main__":
    main()

-ab, bc, ca = (int(i) for i in input().split()) -print((ab * bc // 2)) +def main(): +    a, b, c = (int(i) for i in input().split()) +    from math import sqrt + +    s = (a + b + c) / 2 +    print((int(sqrt(s * (s - a) * (s - b) * (s - c))))) + + +if __name__ == "__main__": +    main()