E

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


int crawl(int n, int m)
{
    int rows = n / 3;
    if (n % 3) ++rows;
    return (n - rows) * m;
}


int main()
{
    int n, m;
    cin >> n >> m;
    cout << max(crawl(n, m), crawl(m, n));
    return 0;
}