rrr

#include <iostream>
using namespace std;

int main()
{
	int a, b;
	cin >> a >> b;
	int sum = 0;
	int sr = 0;
	int c = 0;
	for (int i = 0; a <= b; i++)
	{
		if (b % 2 == 0)
		{
			sum += b;
			c++;
		}
		b--;
	}
	sr = sum / c;
	cout << sr;
}