import java.io.*;
import java.util.*;
import java.text.*;
import java.math.*;
import java.util.regex.*;

public class Solution {

    public static void main(String[] args) {
        Scanner scanner = new Scanner(System.in);
        int factor1 = scanner.nextInt();
        int factor2 = scanner.nextInt();
        int time = scanner.nextInt();
        
       double numnerOfCellExpected = factor1*0.5*1 + factor2*0.5*1;
        
        System.out.println((int)numnerOfCellExpected);
    }
}