#include<cstdio>
#include<cstring>
#include<cctype>
#include<cmath>
#include<climits>
#include<algorithm>
#include<vector>
#include<valarray>
#include<string>
#include<set>
#include<map>
#include<stack>
#include<queue>
using namespace std;
  
  
#define rep(i,n) for(int i=0;i<n;i++)
#define REP(i,n) for(int i=1;i<=n;i++)
#define drep(i,n) for(int i=n-1;i>=0;i--)
#define DREP(i,n) for(int i=n;i>0;i--)
#define Rep(i,m,n) for(int i=m;i<n;i++)
#define scani(a) scanf("%d",&a)
#define scand(a) scanf("%lf",&a)
#define scans(s) scanf("%s",s)
#define printi(a) printf("%d",a)
#define prints(s) printf("%s",s)
#define LF printf("\n")
#define pb push_back
#define mp make_pair
#define bs binary_search
#define all(a) (a).begin(),(a).end()
#define MOD 100000007
  
typedef long long LL;
typedef vector<int> vi;
typedef vector<vector<int> > vvi;
typedef pair<double,double> pdd;
typedef pair<int,int> pii;
  
const double pi=acos(-1.0);
double rad(double t){return t*pi/180.0;}
  
int main(){
  int R,C;
  LL ans;
  scani(R);scani(C);
  if(R==C){
    if(R%2){
      ans = ((LL)R/2)*((LL)R/2+1);
    }else{
      ans = ((LL)R)*(LL)R/4-1;
    }
  }else{
    if(R%2 && C%2){
      ans = ((LL)C)*(R/2)+((LL)C/2);
    }else{
      ans = (LL)R*(LL)C/2-1;
    }
  }
  printf("%lld\n",ans);
  return 0;
}