#include <iostream>

#include <cstdlib>

using namespace std;

int main()

{

   int a,b,k;

   cin>>a>>b;

   bool c;

   c=a%2==1 && b%2==1;

   k=(b-a)/2+1-c;

   cout<<k;

 

 

   //system("pause");

   return 0;

}