import java.util.Scanner;

public class Main {

	@SuppressWarnings("resource")
	public static void main(String args[]) {
		Scanner scanner = new Scanner(System.in);
		int x=scanner.nextInt();
		int y=scanner.nextInt();
		int d=scanner.nextInt();
		long cnt=0;
		for(int i=0;i<=x;i++) {
			for(int j=0;j<=y;j++) {
				if(Math.abs(x-i)+Math.abs(y-j)==d) {
					cnt++;
				}
			}
		}
		System.out.println(cnt);
	}
}