using System;
using System.Linq;
using System.IO;
using System.Collections.Generic;
using System.Text;

namespace AtCoder {
    public class Program {
        static int[] getKeys(char delimiter=' ') {
            var Keys = Console.ReadLine().Split(delimiter);
            int N = Keys.Length;
            int[] Ns = new int[N];
            for (int i = 0; i < N; i++) {
                Ns[i] = int.Parse(Keys[i]);
            }
            return Ns;
        }
        static long[] getKeys_L(char delimiter = ' ') {
            var Keys = Console.ReadLine().Split(delimiter);
            int N = Keys.Length;
            long[] Ns = new long[N];
            for (int i = 0; i < N; i++) {
                Ns[i] = long.Parse(Keys[i]);
            }
            return Ns;
        }
        static double[] getKeys_D(char delimiter = ' ') {
            var Keys = Console.ReadLine().Split(delimiter);
            int N = Keys.Length;
            var Ns = new double[N];
            for (int i = 0; i < N; i++) {
                Ns[i] = double.Parse(Keys[i]);
            }
            return Ns;
        }
        static int[] getLines(int N, char delimiter = ' ') {
            int[] Ns = new int[N];
            for (int i = 0; i < N; i++) {
                Ns[i] = int.Parse(Console.ReadLine());
            }
            return Ns;
        }
        static long[] getLines_L(int N, char delimiter = ' ') {
            long[] Ns = new long[N];
            for (int i = 0; i < N; i++) {
                Ns[i] = long.Parse(Console.ReadLine());
            }
            return Ns;
        }
        static double[] getLines_D(int N, char delimiter = ' ') {
            double[] Ns = new double[N];
            for (int i = 0; i < N; i++) {
                Ns[i] = double.Parse(Console.ReadLine());
            }
            return Ns;
        }

        public static void Show<T>(T[,] map) {
            int H = map.GetLength(0);
            int W = map.GetLength(1);
            Console.WriteLine("-------------------------");
            for (int i = 0; i < H; i++) {
                for (int j = 0; j < W; j++) {
                    Console.Write(map[i, j] + " ");
                }
                Console.WriteLine();
            }
            Console.WriteLine("-------------------------");
        }
        public static void Show<T>(T[,] map, string delimiter) {
            int H = map.GetLength(0);
            int W = map.GetLength(1);
            Console.WriteLine("-------------------------");
            for (int i = 0; i < H; i++) {
                for (int j = 0; j < W; j++) {
                    Console.Write(map[i, j] + delimiter);
                }
                Console.WriteLine();
            }
            Console.WriteLine("-------------------------");
        }
        public static void Show<T>(IEnumerable<T> ts) {
            foreach (var item in ts) {
                Console.Write(item + " ");
            }
            Console.WriteLine();
        }
        public static void Show<T>(IEnumerable<T> ts, string delimiter) {
            foreach (var item in ts) {
                Console.Write(item + delimiter);
            }
            Console.WriteLine();
        }
        public static void ShowDictionary<T1, T2>(Dictionary<T1, T2> dictionary) {
            foreach (var item in dictionary) {
                Console.WriteLine(item);
            }
        }
        static T[] getUniform<T>(int length, T value) {
            T[] Ts = new T[length];
            for (int i = 0; i < length; i++) {
                Ts[i] = value;
            }
            return Ts;
        }
        static void setUniform<T>(T[] ts, T value) {
            int length = ts.Length;
            for (int i = 0; i < length; i++) {
                ts[i] = value;
            }
        }
        static T[,] getUniform<T>(int row, int col, T value) {
            T[,] Ts = new T[row, col];
            for (int i = 0; i < row; i++) {
                for (int j = 0; j < col; j++) {
                    Ts[j, i] = value;
                }
            }
            return Ts;
        }
        static void setUniform<T>(T[,] ts, T value) {
            int N = ts.GetLength(0);
            int M = ts.GetLength(1);
            for (int i = 0; i < M; i++) {
                for (int j = 0; j < N; j++) {
                    ts[j, i] = value;
                }
            }
        }

        static void Main() {
            var key = getKeys();
            int abs = Math.Abs(key[0] - key[1]);
            if (abs > 1) {
                Console.WriteLine(0);
                return;
            }
            long divider = 1000000007;
            long dogs = 1, monkey = 1;
            for (int i = 1; i <= key[0]; i++) {
                dogs *= i;
                dogs %= divider;
            }
            for (int i = 1; i <= key[1]; i++) {
                monkey *= i;
                monkey %= divider;
            }
            long m = abs == 1 ? 1 : 2;
            long answer = ((dogs * monkey) % divider * m) % divider;
            Console.WriteLine(answer);
        }
    }
}

Measured memory_bytes: 13140