import core.bitop;
import std.algorithm;
import std.ascii;
import std.bigint;
import std.conv;
import std.functional;
import std.format;
import std.math;
import std.numeric;
import std.range;
import std.stdio;
import std.string;
import std.random;
import std.typecons;

alias sread = () => readln.chomp();
alias Point2 = Tuple!(long, "y", long, "x");

T lread(T = long)()
{
    return readln.chomp.to!T();
}

T[] aryread(T = long)()
{
    return readln.split.to!(T[])();
}

void scan(TList...)(ref TList Args)
{
    auto line = readln.split();
    foreach (i, T; TList)
    {
        T val = line[i].to!(T);
        Args[i] = val;
    }
}

enum MOD = (10 ^^ 9) + 7;

void main()
{
    long N, M;
    scan(N, M);
    long f(long x)
    {
        long ans = 1;
        foreach (i; 1 .. x + 1)
        {
            ans = (ans * i) % MOD;
        }
        return ans;
    }

    if (N == M)
    {
        writeln((f(N) ^^ 2 % MOD) * 2 % MOD);
    }
    else if (abs(N - M) == 1)
    {
        writeln(f(N) * f(M) % MOD);
    }
    else
    {
        writeln(0);
    }
}
