#include <bits/stdc++.h>
using namespace std;
const int INF = INT_MAX;
const long double PI = 3.1415926535897932384626433;
const long double E = 2.71828183;
const int MOD = 1e9 + 7;
vector<int> bfs(vector<vector<int> > adj, int src) {
  queue<int> q;
  q.push(src);
  vector<int> dst(adj.size(), INF);
  dst[src] = 0;
  while (!q.empty()) {
    int c = q.front();
    q.pop();
    for (int nbr : adj[c]) {
      if (dst[nbr] == INF) {
        dst[nbr] = dst[c] + 1;
        q.push(nbr);
      }
    }
  }
  return dst;
}
vector<int> bfsParents(vector<vector<int> > adj, int src) {
  vector<int> parents = vector<int>(adj.size(), INF);
  parents[src] = -1;
  queue<int> q;
  q.push(src);
  vector<int> dst(adj.size(), INF);
  dst[src] = 0;
  while (!q.empty()) {
    int c = q.front();
    q.pop();
    for (int nbr : adj[c]) {
      if (dst[nbr] == INF) {
        parents[nbr] = c;
        dst[nbr] = dst[c] + 1;
        q.push(nbr);
      }
    }
  }
  return parents;
}
vector<int> shortestPath(vector<vector<int> > adj, int src, int dst) {
  vector<int> bfsParetns = bfsParents(adj, src);
  vector<int> ans;
  while (src != dst) {
    if (bfsParetns[src] == INF) return {};
    ans.push_back(src);
    src = bfsParetns[src];
  }
  return ans;
}
int powMod(int base, int exp, int mod) {
  int ans = 1;
  for (int i = 0; i < exp; i++) ans = ((ans % mod) * (base % mod)) % mod;
  return ans;
}
vector<int> divisorsOf(int n) {
  vector<int> ans;
  for (int i = 1; i * i <= n; i++) {
    if (n % i == 0) ans.push_back(i);
    if (i * i != n && i != 1) ans.push_back(n / i);
  }
  return ans;
}
int gcd(int a, int b) {
  if (a % b == 0)
    return b;
  else
    return gcd(b, a % b);
}
long double log(long double a, long double b) { return log(b) / log(a); }
void solve();
int main() {
  ios_base::sync_with_stdio(false);
  cin.tie(NULL);
  int t;
  solve();
  return 0;
}
void solve() {
  unsigned long long h, w;
  cin >> h >> w;
  if (h == 1 || w == 1) {
    cout << "1\n";
    return;
  }
  if (h % 2 == 0 || w % 2 == 0)
    cout << h * w / 2 << "\n";
  else
    cout << h * w / 2 + 1 << "\n";
}
