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

int main(){
  using ll=long long;
  ll n,m;
  cin>>n>>m;
  ll ans=0;
  if (n%2==0) ans=n*m;
  else if (n==1){
    ans=0;
  }
  else{
    ll top=1;
    while (top*2<=m) top*=2;
    ll bit=1;
    ll sum=0;
    while (bit!=top){
      if (m&bit){
        ans=max(ans,m*(n-2)+(top+bit-1)+(bit+sum));
      }
      else{
        sum+=bit;
      }
      bit*=2;
    }
  }
  cout<<ans<<endl;
}