#include <bits/stdc++.h>
using namespace std;

using ll = long long;

bool chmin(auto &a, auto b) { return a > b ? a = b, true : false; }
bool chmax(auto &a, auto b) { return a < b ? a = b, true : false; }

int main() {
    ios::sync_with_stdio(false);
    cin.tie(nullptr);
    ll N, M;
    cin >> N >> M;
    if (N % 2 == 0) {
        cout << N * M << endl;
        return 0;
    }
    if (N == 1) {
        cout << 0 << endl;
        return 0;
    }
    ll A = 0, B = 0;
    for (int i = 29; i >= 0; i--) {
        if (M >> i & 1) {
            A ^= 1 << i;
            swap(A, B);
        }
    }
    for (int i = 29; i >= 0; i--) {
        ll NA = A ^ (1 << i);
        ll NB = B ^ (1 << i);
        if (NA <= M && NB <= M) {
            A = NA, B = NB;
        }
    }
    cout << max((N - 1) * M, (N - 2) * M + A + B) << endl;
}