a,b=map(int,input().split())
c=len([i for i in range(1,a+1) if i%2==0])
d=len([i for i in range(1,a+1) if i%2!=0])
e=len([i for i in range(1,b+1) if i%2==0])
f=len([i for i in range(1,b+1) if i%2!=0])
if a%2==0 and b%2==0:
    print((a*b)//2)
elif a%2==0 and b%2!=0:
    print((a//2)*b)
elif a%2!=0 and b==0:
    print((b//2)*a)
else:
    print(d*f+c*e)