#include<iostream>
using namespace std;

long long n,m,ans;

int main()
{
   cin>>n>>m;
   
   while(m*n>=2)
   {       
      ans++;
      m--;
      n--;
       
      if(n>=m)n--;
      else    m--;
   }
   
   cout<<ans*2<<endl;
    
   return 0;
}

/*

1000000000000000000 1000000000000000000

int main()
{
   cin>>n>>m;
   
   while(m*n>=2)
   {
      ans++;
      m--;
      n--;
       
      if(n>=m)n--;
      else    m--;
   }
   
   cout<<ans*2<<endl;
    
   return 0;
}*/