#include <bits/stdc++.h>

using namespace std;

#define FOR(i,a,b) for(int i=(a);i<(b);i++)
#define REP(i,n) FOR(i,0,n)
#define ALL(v) (v).begin(),(v).end()

template<typename A, typename B> inline bool chmax(A &a, B b) { if (a<b) { a=b; return 1; } return 0; }
template<typename A, typename B> inline bool chmin(A &a, B b) { if (a>b) { a=b; return 1; } return 0; }

typedef unsigned long long ull;
typedef long long ll;
typedef pair<int, int> pii;
typedef pair<ll, ll> pll;
typedef pair<int, pii> P;

const ll INF = 1ll<<29;
const ll MOD = 1000000007;
const double EPS  = 1e-10;

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