#include<iostream>
using namespace std;
void change(int a,int b)
{
  if((a<0||b<0)
      {
       cout<<"Invalid input";
      }
      else
      {
          cout<<"Invalid input";
          if((!(a%2==0) && (!(b%2==0)))
        {
          cout<<a+b; 
        }
        else if(((a%2==0) && (!(b%2==0))) || ((!(a%2==0)) && (b%2==0)))
        {
            cout<<a-b;
        }
        else
        {
            cout<<"Invalid input"<<endl;
        }
      }  
}
int main()
{
    int a,b;
    cin>>a;
    cin>>b;
    change(a,b);
    return 0;
}