#include <iostream>
using namespace std;

int main() {
	int x, y, sum = 0;
	cin >> x >> y;
	if (x > y) {
		int temp = 0;
		if (x % 2 == 0)
		{
			temp = x / 2;
			sum += temp + temp / 2 - 1;
		}
		else if (x % 2 == 1) {
			temp = x / 2 + 1;
			sum += temp + temp / 2 - 1;
		}
	}
	else if (y > x)
	{
		int temp = 0;
		if( y % 2 == 0)
		{
			temp = y / 2;
			sum += temp + temp / 2 - 1;
		}
		else if (y % 2 == 1) {
			temp = y / 2 + 1;
			sum += temp + temp / 2 - 1;
		}
	}
	cout << sum;
	system("pause");
}