def main():

    H, W = map(int, input().split())
    ans = 0
    if W % 2 == 0 and H % 2 == 0:
        return (W//2) * (H//2) + (W//2) * (H//2)
    if W % 2 == 1 and H % 2 == 0:
        return ((W+1)//2) * (H//2) + (W//2) * (H//2)
    if W % 2 == 0 and H % 2 == 1:
        return (W//2) * ((H+1)//2) + (W//2) * (H//2)
    if W % 2 == 1 and H % 2 == 1:
        return ((W+1)//2) * ((H+1)//2) + (W//2) * (H//2)

if __name__ == '__main__':
    print(main())
