#define _CRT_SECURE_NO_WARNINGS
#include <iostream>
#include <cstdio>
#include <cstring>
#include <ctime>
#include <string>
#include <vector>
#include <stack>
#include <queue>
#include <map>
#include <set>
#include <algorithm>
#include <cmath>
#include <sstream>
using namespace std;
typedef long long ll;
typedef vector<int> vi;
typedef vector<vi> vvi;
#define all(c) (c).begin(), (c).end()
#define loop(i,a,b) for(ll i=a; i<ll(b); i++)
#define rep(i,b) loop(i,0,b)
#ifdef DEBUG
#define dump(...) (cerr<<#__VA_ARGS__<<" = "<<(DUMP(),__VA_ARGS__).str()<<" ["<<__LINE__<<"]"<<endl)
struct DUMP:ostringstream{template<class T>DUMP &operator,(const T&t){if(this->tellp())*this<<", ";*this<<t;return *this;}};
#else
#define dump(...)
#endif

ll solve(ll w, ll h){
    if(h==w){
        if(w&1) return (h/2)*(h/2) + h/2 + 1;
        else return (h/2)*(h/2);
    }else{
        if((h&1) ^ (w&1)){
            if(h&1) swap(h,w);
            // h <- E, w <\-O
            // throw "";
            return h/2*w;
        } else if(h&1 && w&1){
            // throw "";
            return w*h/2 + 1;
        } else{
            //throw "koko wakaran";
            return (w/2)*(h);
        }
    }
    throw "";
    return -1;
}

int main(){
    ll h,w;
    while(cin>>h>>w){
        cout << solve(h,w)-1 << endl;
    }
}