using System;
using System.Linq;
using System.Collections.Generic;

namespace Contest
{
    class Program
    {
        static void Main(string[] args)
        {
            ARC076.C();
        }

        class ARC076
        {
            public static void C()
            {
                var N = Read.Int();
                var M = Read.Int();
                if (Math.Abs(N - M) > 1) { Console.WriteLine(0);return; }
                long ans = 1;
                long P = 1000000007;
                for (int i = 1; i <= N; ++i)
                {
                    ans = (ans * i) % P;
                }
                for (int i = 1; i <= M; ++i)
                {
                    ans = (ans * i) % P;
                }
                if (N == M) { ans = (ans * 2) % P; }
                Console.WriteLine(ans);
            }
            public static void D()
            {
                var N = Read.Int();
                var XY = Read.TupleLong(N);
                Tuple<long, int>[] X = Enumerable.Range(0, N).Select(i => new Tuple<long, int>(XY[i].Item1, i)).ToArray();
                Tuple<long, int>[] Y = Enumerable.Range(0, N).Select(i => new Tuple<long, int>(XY[i].Item2, i)).ToArray();
                Array.Sort(X, (a, b) => a.Item1.CompareTo(b.Item1));
                Array.Sort(Y, (a, b) => a.Item1.CompareTo(b.Item1));
                List<Tuple<long, int, int>> edge = new List<Tuple<long, int, int>>();
                for(int i = 0; i < N - 1; ++i)
                {
                    edge.Add(new Tuple<long, int, int>(X[i + 1].Item1 - X[i].Item1, X[i].Item2, X[i + 1].Item2));
                    edge.Add(new Tuple<long, int, int>(Y[i + 1].Item1 - Y[i].Item1, Y[i].Item2, Y[i + 1].Item2));
                }
                var sortedEdge = edge.ToArray();
                Array.Sort(sortedEdge, (a, b) => a.Item1.CompareTo(b.Item1));
                var uft = new Util.UnionFindTree(N);
                long sum = 0;
                foreach(var e in sortedEdge)
                {
                    if (uft.Root(e.Item2) != uft.Root(e.Item3))
                    {
                        uft.Unite(e.Item2, e.Item3);
                        sum += e.Item1;
                    }
                }
                Console.WriteLine(sum);
            }
        }



        class Util
        {
            public class UnionFindTree
            { //各Treeのサイズを保持する拡張仕様
                int[] parent;
                int[] count;
                public UnionFindTree(int n) { parent = new int[n]; count = new int[n]; for (int i = 0; i < n; ++i) { parent[i] = i; count[i] = 1; } }
                public int Root(int i) { if (parent[i] == i) { return i; } else { return parent[i] = Root(parent[i]); } }
                public int Count(int i) { return count[Root(i)]; }
                public bool Same(int i, int j) { return Root(i) == Root(j); }
                public void Unite(int i, int j) { var ri = Root(i); var rj = Root(j); if (ri != rj) { parent[ri] = rj; count[rj] += count[ri]; } }
            }

        }


        static class Read
        {
            static Queue<string> queue = new Queue<string>();
            static void Enqueue() { var ss = Console.ReadLine().Split(' '); foreach (var s in ss) { queue.Enqueue(s); } }
            public static int Int() { if (queue.Count == 0) { Enqueue(); } return Convert.ToInt32(queue.Dequeue()); }
            public static long Long() { if (queue.Count == 0) { Enqueue(); } return Convert.ToInt64(queue.Dequeue()); }
            public static string Str() { if (queue.Count == 0) { Enqueue(); } return queue.Dequeue(); }
            public static int[] IntN() { return Console.ReadLine().Split(' ').Select(s => Convert.ToInt32(s)).ToArray(); }
            public static long[] LongN() { return Console.ReadLine().Split(' ').Select(s => Convert.ToInt64(s)).ToArray(); }
            public static string[] StrN() { return Console.ReadLine().Split(' '); }
            public static Tuple<int, int>[] TupleInt(int n) { List<Tuple<int, int>> list = new List<Tuple<int, int>>(); for (int i = 0; i < n; ++i) { var ab = Read.IntN(); list.Add(new Tuple<int, int>(ab[0], ab[1])); } return list.ToArray(); }
            public static Tuple<long, long>[] TupleLong(int n) { List<Tuple<long, long>> list = new List<Tuple<long, long>>(); for (int i = 0; i < n; ++i) { var ab = Read.LongN(); list.Add(new Tuple<long, long>(ab[0], ab[1])); } return list.ToArray(); }
            public static Tuple<string, string>[] TupleStr(int n) { List<Tuple<string, string>> list = new List<Tuple<string, string>>(); for (int i = 0; i < n; ++i) { var ab = Read.StrN(); list.Add(new Tuple<string, string>(ab[0], ab[1])); } return list.ToArray(); }
            public static Tuple<double, double>[] TupleDouble(int n) { List<Tuple<double, double>> list = new List<Tuple<double, double>>(); for (int i = 0; i < n; ++i) { var ab = Read.LongN(); list.Add(new Tuple<double, double>(ab[0], ab[1])); } return list.ToArray(); }
            public static long[,] LongMatrix(int r, int c)
            {
                var mat = new long[r, c];
                for (int i = 0; i < r; ++i)
                {
                    var x = Read.LongN();
                    for (int j = 0; j < c; ++j)
                    {
                        mat[i, j] = x[j];
                    }
                }
                return mat;
            }
            public static Dictionary<int, HashSet<int>> AdjacencyList(int N, int M)
            {
                Dictionary<int, HashSet<int>> dict = new Dictionary<int, HashSet<int>>();
                for (int i = 0; i <= N; ++i)
                {
                    dict.Add(i, new HashSet<int>());
                }
                for (int i = 0; i < M; ++i)
                {
                    var ab = Read.IntN();
                    dict[ab[0]].Add(ab[1]);
                    dict[ab[1]].Add(ab[0]);
                }
                return dict;
            }
            public static Dictionary<int, Dictionary<int, long>> AdjacencyListWithWeight(int N, int M)
            {
                Dictionary<int, Dictionary<int, long>> dict = new Dictionary<int, Dictionary<int, long>>();
                for (int i = 0; i <= N; ++i)
                {
                    dict.Add(i, new Dictionary<int, long>());
                }
                for (int i = 0; i < M; ++i)
                {
                    var ab = Read.IntN();
                    dict[ab[0]].Add(ab[1], ab[2]);
                    dict[ab[1]].Add(ab[0], ab[2]);
                }
                return dict;
            }
        }
    }
}


Measured memory_bytes: 13396