a?

#include <bits/stdc++.h>
using namespace std;
int main()
{
	int n,m;
	scanf("%d%d",&n,&m);
	if(n<2 and m<2)
	{
		cout<<0;
		return 0;
	}
	int a[n][m];
	memset(a,0,sizeof(a));
	int cnt=0;
	for(int i=0;i<n;i++)
	{
		for(int j=0;j<m;j++)
		{
			if(a[i][j]==0 and a[i][j+1]==0)
			{
				cnt++;
				a[i][j]=1;
				a[i][j+1]=1;
			}
			else if(a[i][j]==0 and a[i][j-1]==0)
			{
				cnt++;
				a[i][j]=1;
				a[i][j-1]=1;
			}
			else if(a[i][j]==0 and a[i+1][j])
			{
				cnt++;
				a[i][j]=1;
				a[i+1][j]=1;
			}
			else if(a[i][j]==0 and a[i-1][j]==0)
			{
				cnt++;
				a[i][j]=1;
				a[i-1][j]=1;
			}
            /*for(int k=0;k<n;k++)
            {
                for(int o=0;o<m;o++)
                {
                    cout<<a[i][j]<<" ";
                }
                cout<<endl;
            }
            cout<<endl;*/
		}
	}
	cout<<cnt;
}