# include <iostream>
using namespace std;
int main ()
{
long long n,m,br=0;
cin>>n>>m;
while(n>2&&m>2)
{
    if(n>m)swap(n,m);
    n-=1;
    m-=2;
    br+=2;
}
if(n>m)swap(n,m);
if(n==1)cout<<br+2<<endl;
if(n==2)
{
    if(m<4)cout<<br+2<<endl;
    if(m>=4)cout<<br+4<<endl;
}
return 0;
}