#include <iostream>
#include <vector>
#include <algorithm>
using namespace std;

#define RREP(i,s,e) for (i = e-1; i >= s; i--)
#define rrep(i,n) RREP(i,0,n)
#define REP(i,s,e) for (i = s; i < e; i++)
#define rep(i,n) REP(i,0,n)
#define INF 1e8

typedef long long ll;

int main() {
    ll r, c;
    cin >> r >> c;
    if (r == c)
        cout << (r * c - 1) / 4 << endl;
    else
        cout << ((c+1)/2) * ((r+1)/2) + (c/2) * (r/2) - 1 << endl;
    return 0;
}