import java.util.*;
class AtCoder {
public static void main(String[] args) {
Scanner in = new Scanner(System.in);
try{
long n, a, b;
n = in.nextLong();
a = in.nextLong();
b = in.nextLong();
if ((b - a) % 2 == 0)
System.out.println((b - a) / 2);
else
System.out.println(b - 1);
in.close();
}catch(Exception e)
{
return;
}
}
}