import javax.smartcardio.CommandAPDU;
import java.io.* ;
import java.lang.reflect.Array;
import java.util.* ;
import java.math.* ;
public class Main
{
    static BufferedReader reader;
    static StringTokenizer tokenizer;

    static void init(InputStream input)
    {
        reader = new BufferedReader(new InputStreamReader(input));
        tokenizer = new StringTokenizer("");
    }

    static String next() throws IOException
    {
        while (!tokenizer.hasMoreTokens())
        {
            tokenizer = new StringTokenizer(reader.readLine());
        }
        return tokenizer.nextToken();
    }

    static long nextInt() throws IOException
    {
        return Long.parseLong(next());
    }

    public static int ri() throws IOException
    {
        return (int) nextInt();
    }

    public static long rl() throws IOException
    {
        return nextInt();
    }

    public static double rd() throws NumberFormatException, IOException
    {
        return Double.parseDouble(next());
    }

    static void print_a(int[] arr)
    {
        for (int i = 0; i < arr.length; i++)
        {
            print(arr[i] + " ");
        }
        println();
    }

    public static int[] ria(int n) throws IOException
    {
        int[] a = new int[n];
        for (int i = 0; i < n; i++)
        {
            a[i] = ri();
        }
        return a;
    }

    public static long[] rla(int n) throws IOException
    {
        long[] a = new long[n];
        for (int i = 0; i < n; i++)
        {
            a[i] = rl();
        }
        return a;
    }

    public static int p(int i)
    {
        return (int) Math.pow(2, i);
    }

    static PrintWriter writer;

    static void outit(OutputStream outputStream)
    {
        writer = new PrintWriter(new BufferedWriter(new OutputStreamWriter(outputStream)));
    }

    static void print(Object... objects)
    {
        for (int i = 0; i < objects.length; i++)
        {
            if (i != 0)
                writer.print(' ');
            writer.print(objects[i]);
        }
    }

    static void println(Object... objects)
    {
        print(objects);
        writer.println();
        flush();
    }

    static void close()
    {
        writer.close();
    }

    static void flush()
    {
        writer.flush();
    }

    public static void main(String[] args) throws IOException
    {
        init(System.in);
        outit(System.out);
//        int t = (int) nextInt();
//        for (int i = 0; i < t; i++)
        output();
        flush();
        close();
    }
    static long mod = 1000000007;
    static long [] fact ;
    public static void output() throws IOException
    {
        int n = ri() ;
        int m = ri() ;
        precompute();
        if(n>(m+1)||m>(n+1))
        {
            println(0) ;
        }
        else if(n==m)
        {
            println((2*fact[n]*fact[m])%mod) ;
        }
        else if(n==m+1||m==n+1)
        {
            println((fact[n]*fact[m])%mod) ;
        }
        else
        {
            println(0) ;
        }
    }
    static void precompute()
    {
        fact = new long[100001] ;
        fact[0] = 1 ;
        for (long i = 1; i <=100000 ; i++)
        {
            fact[(int)i] = (fact[(int)(i-1)]*i)%mod ;
        }
    }
}

Measured memory_bytes: 22996