import std.algorithm;
import std.array;
import std.ascii;
import std.bigint;
import std.complex;
import std.container;
import std.conv;
import std.functional;
import std.math;
import std.range;
import std.stdio;
import std.string;
import std.typecons;

auto readInts() {
	return array(map!(to!int)(readln().strip().split()));
}
auto readInt() {
	return readInts()[0];
}
auto readLongs() {
	return array(map!(to!long)(readln().strip().split()));
}
auto readLong() {
	return readLongs()[0];
}

void readlnTo(T...)(ref T t) {
    auto s = readln().split();
    assert(s.length == t.length);
    foreach(ref ti; t) {
        ti = s[0].to!(typeof(ti));
        s = s[1..$];
    }
}

const real eps = 1e-10;

const long p = 1_000_000_000 + 7;

//n!
long P(long n) {
    if(n == 0) {
        return 1;
    }
    return n * P(n-1) % p;
}

void main(){
    long n, m;
    readlnTo(n, m);

    if(abs(n-m) > 1) {
        writeln(0);
        return;
    }

    writeln((P(n) * P(m) % p) * (n == m ? 2: 1) % p);
}

