#include <bits/stdc++.h>
using namespace std;
template <typename T>
bool get_int(T &x) {
  char t = getchar();
  bool neg = false;
  x = 0;
  for (; (t > '9' || t < '0') && t != '-' && t != EOF; t = getchar())
    ;
  if (t == '-') neg = true, t = getchar();
  if (t == EOF) return false;
  for (; t <= '9' && t >= '0'; t = getchar()) x = x * 10 + t - '0';
  if (neg) x = -x;
  return true;
}
template <typename T>
void print_int(T x) {
  if (x < 0) putchar('-'), x = -x;
  short a[20] = {}, sz = 0;
  while (x > 0) a[sz++] = x % 10, x /= 10;
  if (sz == 0) putchar('0');
  for (int i = sz - 1; i >= 0; i--) putchar('0' + a[i]);
}
const int inf = 0x3f3f3f3f;
const long long Linf = 1ll << 61;
const double pi = acos(-1.0);
int n, m;
int main() {
  (get_int(n) && get_int(m));
  if (n > m) swap(n, m);
  if (n == 1) {
    int ans = 0;
    for (int i = 0; i < 3; i++) {
      if (i < m % 3)
        ans += (m / 3 + 1) / 2 * 2;
      else
        ans += m / 6 * 2;
    }
    print_int(ans), puts("");
  } else if (n == 2 && m == 2)
    puts("0");
  else if (n == 2 && m == 3)
    puts("4");
  else if (n == 2 && m == 7)
    puts("12");
  else
    printf("%I64d\n", 1ll * n * m / 2 * 2);
  return 0;
}
