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

namespace ARC076C2
{
    class Program
    {
        public static void Solve(Input input)
        {
            var n = input.NextInt();
            var m = input.NextInt();

            if (Math.Abs(m - n) >= 2)
            {
                // 隣り合わない組み合わせが存在しない
                Console.WriteLine(0);
                return;
            }

            // nPn * mPm
            var ans = new ModInt(1);

            // nPn = n!
            ans *= ModInt.Factorial(n, MOD);
            ans *= ModInt.Factorial(m, MOD);
            if (n == m)
            {
                // 同じ数だけいるなら、どちらを先頭とするかで組み合わせが増える
                ans *= 2;
            }

            Console.WriteLine(ans);
        }

        /// <summary>
        /// Mを法とする数値
        /// Mは素数
        /// </summary>
        public struct ModInt
        {
            public readonly int M;
            private readonly int N;

            /// <summary>
            /// 
            /// </summary>
            /// <param name="n">実際の数値</param>
            /// <param name="mod">M</param>
            public ModInt(int n, int mod = (int)1e9 + 7)
            {
                N = n % mod;
                M = mod;
            }

            [System.Runtime.CompilerServices.MethodImpl(System.Runtime.CompilerServices.MethodImplOptions.AggressiveInlining)]
            public static ModInt Add(int a, int b, int M)
                => new ModInt((a + b) % M, M);

            [System.Runtime.CompilerServices.MethodImpl(System.Runtime.CompilerServices.MethodImplOptions.AggressiveInlining)]
            public static ModInt Sub(int a, int b, int M)
                => new ModInt((a + M - b) % M, M);

            [System.Runtime.CompilerServices.MethodImpl(System.Runtime.CompilerServices.MethodImplOptions.AggressiveInlining)]
            public static ModInt Mul(int a, int b, int M)
                => new ModInt((int)(((long)(a % M) * (b % M)) % M), M);

            /// <summary> a/b </summary>
            [System.Runtime.CompilerServices.MethodImpl(System.Runtime.CompilerServices.MethodImplOptions.AggressiveInlining)]
            public static ModInt Div(int a, int b, int M)
                => Mul(a, Inverse(b, M), M);

            /// <summary>
            /// aの逆元（a^-1）
            /// （厳密には違うが）Mは素数とする
            /// </summary>
            public static ModInt Inverse(int a, int M)
            {
                int b = M;
                int u = 1, v = 0;

                while (b > 0)
                {
                    int t = a / b;
                    a -= t * b;
                    Swap(ref a, ref b);
                    u -= t * v;
                    Swap(ref u, ref v);
                }

                u %= M;
                if (u < 0) u += M;

                return new ModInt(u, M);
            }

            /// <summary>
            /// x^y
            /// 繰り返し二乗法
            /// </summary>
            public static ModInt Power(int a, int b, int M)
            {
                var r = new ModInt(1, M);

                while (b > 0)
                {
                    if ((b & 1) != 0) r = Mul(r, a, M);

                    a = Mul(a, a, M);
                    b >>= 1;
                }

                return r;
            }

            public override string ToString() => N.ToString();

            #region Combinatorics
            /// <summary>
            /// 階乗(n!)
            /// </summary>
            public static ModInt Factorial(int n, int M)
            {
                var fact = new ModInt(1, M);
                while (n > 0)
                {
                    fact *= n;
                    n--;
                }

                return fact;
            }

            /// <summary>
            /// 順列(nPr)
            /// </summary>
            public static ModInt Npr(int n, int r, int M)
            {
                if (n < r || n < 0 || r < 0)
                {
                    return new ModInt(0, M);
                }

                var npr = new ModInt(1, M);
                for (int i = n; i > n - r; i--)
                {
                    npr *= n;
                }

                return npr;
            }

            /// <summary>
            /// 組み合わせ(nCr)
            /// </summary>
            public static ModInt Ncr(int n, int r, int M)
            {
                if (n < r || n < 0 || r < 0)
                {
                    return new ModInt(0, M);
                }

                r = Math.Min(r, n - r);
                var npr = Npr(n, r, M);
                var fact = Factorial(r, M);

                return npr / fact;
            }

            /// <summary>
            /// 重複組み合わせ(nHr)
            /// n個から重複を許してr個取り出す
            /// </summary>
            public static ModInt Nhr(int n, int r, int M)
                => Ncr(n + r - 1, r, M);
            #endregion

            #region Operator, Alias
            [System.Runtime.CompilerServices.MethodImpl(System.Runtime.CompilerServices.MethodImplOptions.AggressiveInlining)]
            public static implicit operator int(ModInt a)
                => a.N;

            [System.Runtime.CompilerServices.MethodImpl(System.Runtime.CompilerServices.MethodImplOptions.AggressiveInlining)]
            public static ModInt operator +(ModInt a, int b)
                => Add(a, b, a.M);

            [System.Runtime.CompilerServices.MethodImpl(System.Runtime.CompilerServices.MethodImplOptions.AggressiveInlining)]
            public static ModInt operator -(ModInt a, int b)
                => Sub(a, b, a.M);

            [System.Runtime.CompilerServices.MethodImpl(System.Runtime.CompilerServices.MethodImplOptions.AggressiveInlining)]
            public static ModInt operator *(ModInt a, int b)
                => Mul(a, b, a.M);

            [System.Runtime.CompilerServices.MethodImpl(System.Runtime.CompilerServices.MethodImplOptions.AggressiveInlining)]
            public static ModInt operator /(ModInt a, int b)
                => Div(a, b, a.M);

            [System.Runtime.CompilerServices.MethodImpl(System.Runtime.CompilerServices.MethodImplOptions.AggressiveInlining)]
            public static ModInt operator +(int a, ModInt b)
                => Add(a, b, b.M);

            [System.Runtime.CompilerServices.MethodImpl(System.Runtime.CompilerServices.MethodImplOptions.AggressiveInlining)]
            public static ModInt operator -(int a, ModInt b)
                => Sub(a, b, b.M);

            [System.Runtime.CompilerServices.MethodImpl(System.Runtime.CompilerServices.MethodImplOptions.AggressiveInlining)]
            public static ModInt operator *(int a, ModInt b)
                => Mul(a, b, b.M);

            [System.Runtime.CompilerServices.MethodImpl(System.Runtime.CompilerServices.MethodImplOptions.AggressiveInlining)]
            public static ModInt operator /(int a, ModInt b)
                => Div(a, b, b.M);

            [System.Runtime.CompilerServices.MethodImpl(System.Runtime.CompilerServices.MethodImplOptions.AggressiveInlining)]
            public static ModInt operator +(ModInt a, ModInt b)
            {
                if (a.M != b.M) throw new ArgumentException();
                return Add(a, b, a.M);
            }

            [System.Runtime.CompilerServices.MethodImpl(System.Runtime.CompilerServices.MethodImplOptions.AggressiveInlining)]
            public static ModInt operator -(ModInt a, ModInt b)
            {
                if (a.M != b.M) throw new ArgumentException();
                return Sub(a, b, a.M);
            }

            [System.Runtime.CompilerServices.MethodImpl(System.Runtime.CompilerServices.MethodImplOptions.AggressiveInlining)]
            public static ModInt operator *(ModInt a, ModInt b)
            {
                if (a.M != b.M) throw new ArgumentException();
                return Mul(a, b, a.M);
            }

            [System.Runtime.CompilerServices.MethodImpl(System.Runtime.CompilerServices.MethodImplOptions.AggressiveInlining)]
            public static ModInt operator /(ModInt a, ModInt b)
            {
                if (a.M != b.M) throw new ArgumentException();
                return Div(a, b, a.M);
            }

            /// <summary> a^b </summary>
            [System.Runtime.CompilerServices.MethodImpl(System.Runtime.CompilerServices.MethodImplOptions.AggressiveInlining)]
            public static ModInt Power(ModInt a, int b)
                => Power(a, b, a.M);

            /// <summary> a^b </summary>
            [System.Runtime.CompilerServices.MethodImpl(System.Runtime.CompilerServices.MethodImplOptions.AggressiveInlining)]
            public static ModInt Power(ModInt a, ModInt b)
            {
                if (a.M != b.M) throw new ArgumentException();
                return Power(a, b, a.M);
            }

            /// <summary> n! </summary>
            [System.Runtime.CompilerServices.MethodImpl(System.Runtime.CompilerServices.MethodImplOptions.AggressiveInlining)]
            public static ModInt Factorial(ModInt n)
                => Factorial(n, n.M);

            #endregion

            #region Misc
            [System.Runtime.CompilerServices.MethodImpl(System.Runtime.CompilerServices.MethodImplOptions.AggressiveInlining)]
            static void Swap<T>(ref T a, ref T b)
            {
                T temp = a;
                a = b;
                b = temp;
            }
            #endregion
        }

        #region Main
        public static void Main(string[] args)
        {
            // 出力が少ないときはこれをセットする方が時間かかるけれど
            // そのときにTLEするのはアルゴリズムが悪いせいだし、まあ良しとする
            var needsFlushOutput = true;
            if (needsFlushOutput)
            {
                // 細かく出力しないようにする
                var sw = new StreamWriter(Console.OpenStandardOutput()) { AutoFlush = false };
                Console.SetOut(sw);
            }

            // 通常は引数無しで、ファイルから読み出したい場合はpath指定する
            var input = new Input();

            // 仮想的に標準入力をセットする
            // テスト入力したまま提出することがままあるので……
#if DEBUG
            input.SetText("");
#endif

            Solve(input);

            Console.Out.Flush();
        }
        #endregion

        #region Competitive Template
#pragma warning disable CS0414
        static readonly int MOD = (int)1e9 + 7;
        static readonly int[] dx = { 1, 0, -1, 0 };
        static readonly int[] dy = { 0, 1, 0, -1 };
        /// <summary> 左上が原点 </summary>
        static readonly char[] dir = { 'R', 'U', 'L', 'D' };
#pragma warning restore CS0414

        public class Input
        {
            // 変な改行コードがたまに混じっているので、一応セパレート指定する
            // スペース単独指定の方がもちろん早い
            static readonly char[] separator = { ' ', '\r', '\n' };
            readonly StreamReader sr;
            readonly Queue<string> queue;

            /// <summary>
            /// 特定のファイルから読み出したい場合はpath指定する
            /// </summary>
            public Input(string path = "")
            {
                queue = new Queue<string>();

                if (string.IsNullOrEmpty(path)) { sr = new StreamReader(Console.OpenStandardInput()); }
                else { sr = new StreamReader(path); }
            }

            /// <summary>
            /// 入力予約
            /// </summary>
            public void SetText(IEnumerable<string> items)
            {
                foreach (var item in items)
                    SetText(item);
            }

            /// <summary>
            /// 入力予約
            /// </summary>
            public bool SetText(string s)
            {
                if (string.IsNullOrEmpty(s)) return false;

                foreach (var elem in s.Trim().Split(separator, StringSplitOptions.RemoveEmptyEntries))
                    queue.Enqueue(elem);

                return true;
            }

            /// <summary>
            /// 要素が存在するか
            /// </summary>
            public bool Any() => queue.Any() || Read();

            /// <summary>
            /// 内部queueに入力からの値をsplitして格納する
            /// </summary>
            bool Read()
            {
                if (!SetText(sr.ReadLine())) return false;

                if (!queue.Any()) return Read();

                return queue.Any();
            }

            /// <summary>
            /// 次のstringを一つ読み込む
            /// </summary>
            public string Next()
            {
                if (!queue.Any() && !Read()) return "";

                return queue.Dequeue();
            }

            /// <summary>
            /// 指定個数queueにたまるまでenqueueし続ける
            /// </summary>
            bool Accumulate(int n)
            {
                while (queue.Count() < n)
                    if (!Read()) return false;

                return true;
            }

            public int NextInt() => int.Parse(Next());
            public long NextLong() => long.Parse(Next());
            public double NextDouble() => double.Parse(Next());

            /// <summary>
            /// n個の要素をparseして、それぞれにoffsetをaddした配列を返す
            /// </summary>
            T[] NextT<T>(int n, T offset, Func<string, T> parse, Func<T, T, T> add)
            {
                if (!Accumulate(n)) return null;

                var a = new T[n];

                for (int i = 0; i < n; i++)
                    a[i] = add(parse(queue.Dequeue()), offset);

                return a;
            }

            public string[] Next(int n) => NextT(n, "", x => x, (x, y) => x);
            public int[] NextInt(int n, int offset = 0) => NextT(n, offset, int.Parse, (x, y) => x + y);
            public long[] NextLong(int n, long offset = 0) => NextT(n, offset, long.Parse, (x, y) => x + y);
            public double[] NextDouble(int n, double offset = 0.0) => NextT(n, offset, double.Parse, (x, y) => x + y);
        }

        static class Utils
        {
            public static T Max<T>(params T[] objs) => objs.Max();
            public static T Min<T>(params T[] objs) => objs.Min();

            /// <summary>
            /// vでfillされたT[d1][d2]配列を作成する
            /// </summary>
            public static T[][] Create2DArray<T>(int d1, int d2, T v)
            {
                return
                    Enumerable.Repeat(0, d1).Select(_ =>
                    Enumerable.Repeat(v, d2).ToArray()).ToArray();
            }

            /// <summary>
            /// vでfillされたT[d1][d2][d3]配列を作成する
            /// </summary>
            public static T[][][] Create3DArray<T>(int d1, int d2, int d3, T v)
            {
                return
                    Enumerable.Repeat(0, d1).Select(_ =>
                    Enumerable.Repeat(0, d2).Select(__ =>
                    Enumerable.Repeat(v, d3).ToArray()).ToArray()).ToArray();
            }
        }
        #endregion
    }
}


Measured memory_bytes: 11348