#include <bits/stdc++.h>
inline int abs(int n) { return n < 0 ? -n : n; }
bool board[20][20];
int dx[] = {-3, -2, -2, -1, -1, 0, 0, 1, 1, 2, 2, 3};
int dy[] = {0, 1, -1, 2, -2, 3, -3, 2, -2, 1, -1, 0};
int dfs(int p, int n, int m) {
  int mx = p, t, cnt = 0;
  for (int i = 0; i < n; i++) {
    for (int j = 0; j < m; j++) {
      if (!board[i][j]) {
        board[i][j] = true;
        for (int k = 0; k < 12; k++) {
          int ic = i + dx[k], jc = j + dy[k];
          if (ic >= 0 && ic < n && jc >= 0 && jc < m && !board[ic][jc]) {
            board[ic][jc] = true;
            t = dfs(p + 2, n, m);
            mx < t && (mx = t);
            if (mx == ((m * n) | 1) - 1) return mx;
            board[ic][jc] = false;
          }
        }
        board[i][j] = false;
        cnt++;
        if (m * n - cnt <= mx) return mx;
      }
    }
  }
  return mx;
}
int ans[] = {0, 0, 0, 0, 2, 4};
int main() {
  int m, n;
  scanf("%d%d", &m, &n);
  if (m < 10 && n < 10) {
    printf("%d\n", dfs(0, n, m));
  } else if (m == 1) {
    printf("%d\n", n / 6 * 6 + ans[n % 6]);
  } else if (n == 1) {
    printf("%d\n", m / 6 * 6 + ans[m % 6]);
  } else {
    printf("%lld\n", (((long long)(m)*n) | 1) - 1);
  }
  return 0;
}
