#include<bits/stdc++.h> 
using namespace std;
int main(){
    int a,b;
    cin>>a>>b;
    if(a-b==2){
    	cout<<0;
    	return 0;
	}
    if(a%2==0&&b%2==0||a%2==1&&b%2==1){
    	cout<<abs((b-a)/2-1);
		return 0; 
	}
	else{
		cout<<abs(b/2+a/2);
		return 0;
	}
	return 0;
}