#define ll long long int
#include <bits/stdc++.h>

using namespace std;

#define         ff               first
#define         ss               second
#define         mp               make_pair
#define         pb               push_back
#define         pf               push_front
#define         vi               vector<ll>
#define         pii              pair<ll,ll>
#define         qi               queue<ll>
#define         mem(a,b)         memset(a,b,sizeof(a))
#define         print(a)         cout<<a<<'\n'
#define         sorted(arr)      sort(arr.begin(),arr.end())
#define         gcd(a,b)         gcd((a),(b))
#define         lcm(a,b)         ((a)*(b))/gcd((a),(b))
#define         all(v)           v.begin(),v.end()
#define         read(a)          scanf("%d", &a)
#define         f(a,n)           for(ll i=a;i<n;i++)
#define         in2(n,m,arr)     for(ll i=0;i<n;i++){for(ll j=0;j<m;j++)cin>>arr[i][j];}
#define         debug(a)         cerr<<a<<" ";
#define         debug1(a)        cerr<<a<<'\n'
 

const unsigned ll mod = 1e9 + 7;
const ll inf = (ll)1e18 + 2;
const ll N = (ll)4e5 + 2;

ll power( ll x , ll y)
{
    ll res = 1;
    while (y > 0)
    {
        if (y & 1)
            res = (res * x) % mod ;
        y = y >> 1;
        x = (x * x) % mod ;
    }
    return res % mod ;
}
double sq(double n){
    double x = n , y = 1 ,  a = 0.0000000001;
    while((x - y)> a)
    {
        x = (x + y)/2;
        y = n / x;
    }
    return x;
}
void solve()
{
    ll x , y;
    cin >> x >>y;
    ll ans = x * y;
    if(y == 1 || x == 1)
    {
        cout << 1 << '\n';
        return;
    }
    ans = (ans + 1)/2;
    print(ans);
}

int main()
{
    ios_base::sync_with_stdio(false);
    cin.tie(0);
    cout.tie(0);
    ll t ;
    t = 1;
    //cin >> t ;
    //seive();
    while(t --)
    {
        solve();
    }
    cerr << "\nTime elapsed: " << 1000 * clock() / CLOCKS_PER_SEC << "ms\n";
    return 0;
}
 

/* ---------------------------------------------------------------------------------------------------------------------



#include <ext/pb_ds/tree_policy.hpp>
#include <ext/pb_ds/assoc_container.hpp>
using namespace __gnu_pbds;
typedef tree<int, null_type, less<int>, rb_tree_tag , tree_order_statistics_node_update> Set;

 
vector<ll> ar ;

ll get(ll x)
{
    if(x == ar[x])
        return x;
    return ar[x] = get(ar[x]);
}
void merge(ll a ,ll b)
{
    a = get(a);
    b = get(b);
    if(a == b)
    {
        return ;
    }
    ar[b] = ar[a];
 }

ll sev[100006];
vector<ll> pri;
void seive()
{
    for(ll i = 2 ; i < 100006 ; i ++)
    {
        if(!sev[i])
        {
            for(ll j = i ; j < 100006 ; j += i)
            {
                if(!sev[j])
                    sev[j] = i;
            }
        }
        if(sev[i] == i)
            pri.pb(i);
    }
}
 
 ll totient(ll n){
     ll result = n;
     for(ll i = 2 ; i * i <= n ; i ++){
         if(n % i == 0){
             while(n % i == 0)
                 n /= i;
             result -= result / i;
         }
     }
     if(n > 1)
         result -= result / n;
     return result;
 }
 
 
 ll fen[N];
 void add(ll idx , ll val){
     idx ++;
     while(idx <= N){
         fen[idx] += val;
         idx += (idx & (-idx));
     }
 }
 ll query(ll idx){
     idx ++;
     ll sum = 0;
     while(idx > 0){
         sum += fen[idx];
         idx -= (idx & (-idx));
     }
     return sum;
 }
 
*/


Measured memory_bytes: 256