import java.io.*;
import java.util.*;

public class Main {
	public static void main(String[] args) throws IOException {
		BufferedReader in = new BufferedReader(new InputStreamReader(System.in));
		PrintWriter out = new PrintWriter(System.out);

		StringTokenizer line = new StringTokenizer(in.readLine());
		int n = Integer.parseInt(line.nextToken());
		int m = Integer.parseInt(line.nextToken());
		
		int l = 1;
		int r = 1000005;
		int min = -1;
		while (l <= r) {
			int mid = (l + r) / 2;
			int nl = Math.max(n - mid * 3, 0);
			int ml = Math.max(m - mid * 3, 0);
			if (mid >= nl + ml) {
				min = mid;
				r = mid - 1;
			} else {
				l = mid + 1;
			}
		}
		out.println(2 * min - 1);

		in.close();
		out.close();
	}
}