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

alias sread = () => readln.chomp();
ulong bignum = 1_000_000_007;
alias Pair = Tuple!(long, "number", long, "times");

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;
    }
}

void main()
{
    long n, m;
    scan(n, m);
    auto dif = abs(n - m);
    if(dif == 1)
    {
        auto set = product_mod(min(n, m));
        set *= set;
        set %= bignum;
        set *= max(n, m);
        set %= bignum;
        set.writeln();
    }
    else if(dif == 0)
    {
        auto set = product_mod(n);
        set *= set;
        set %= bignum;
        set *= 2;
        set %= bignum;
        set.writeln();
    }
    else
        writeln(0);
}

long product_mod(long n)
{
    if(n == 1)
        return 1;

    return n * product_mod(n - 1) % bignum;
}