#include <iostream>

using namespace std;

double Average(double, double);

int main() {
	double input1, input2;
	cin >> input1 >> input2;
	cout << Average(input1, input2) << endl;
}

double Average(const double x, const double y)
{
	double t;
	t = (x + y) / 2.;
	return t;
}