#define ll long long int
#define eb emplace_back
#define mkp make_pair
#define MOD 100000007
int main()
{
    ios_base::sync_with_stdio(false);
    cin.tie(NULL);cout.tie(NULL);
    ll r,c;	cin>>r>>c;
  	ll ans=(r*c)/2;
  	if(r==1 || c==1)cout<<"1";
  	else {
      if(r%2==0 || c%2==0)cout<<ans;
  	  else cout<<ans+1;
    }
}