#include <bits/stdc++.h>
using namespace std;

#define ll long long
#define ull unsigned long long
#define ld long double
#define pll pair<long long,long long>
#define pcc pair<char,char>
#define vl vector<long long>
#define vvl vector<vector<long long>>
#define vvvl vector<vector<vector<long long>>>
#define vc vector<char>
#define vvc vector<vector<char>>
#define vs vector<string>
#define vb vector<bool>
#define vvb vector<vector<bool>>
#define vp vector<pair<long long,long long>>
#define umap unordered_map
#define uset unordered_set
#define Lqueue priority_queue<long long>
#define Squeue priority_queue<long long,vector<long long>,greater<long long>>
#define fi first
#define se second
#define mp make_pair
#define mt make_tuple
#define eb emplace_back

const int MOD1=1000000007;
const int MOD2=998244353;
const long double PI=3.1415926535897932;
const long long MAXLL=9223372036854775807;
const long long INF=2305843009213693951;
const int dx[]={0,1,0,-1,1,-1,1,-1};
const int dy[]={1,0,-1,0,1,1,-1,-1};

#define unless(a) if(!(a))
#define all(x) (x).begin(),(x).end()
#define rall(x) (x).rbegin(),(x).rend()
#define rbf(a,x) for(auto& a:x)
#define rep(i,n) for(int i=0;i<(n);i++)
#define rep2(i,s,n) for(int i=(s);i<(n);i++)
#define bitrep(i,s,n) for(int i=(s);i<(1LL<<(n));i++)
#define bitcheck(bit,i) (bit)&(1LL<<(i))
#define Maxe(x) *max_element((x).begin(),(x).end())
#define Mine(x) *min_element((x).begin(),(x).end())
#define Size(x) ((long long)(x).size())
#define Lin(s) getline(cin,(s))

void Yes(bool a){cout<<(a?"Yes":"No")<<endl;}
void YES(bool a){cout<<(a?"YES":"NO")<<endl;}
template<class T,class U> auto max(T a,U b){return a>b?a:b;}
template<class T,class U> auto min(T a,U b){return a<b?a:b;}
long long gcd(long long a,long long b){return b?gcd(b,a%b):a;}
long long lcm(long long a,long long b){return a/gcd(a,b)*b;}
long long cutup(long long a,long long b){return (a+b-1)/b;}
long long popcnt(long long a){return __builtin_popcountll(a);}
template<class T,class U> inline bool chmin(T& a,U b){if(a>b){a=b;return true;}return false;}
template<class T,class U> inline bool chmax(T& a,U b){if(a<b){a=b;return true;}return false;}

struct edge{long long to,cost;};
struct edge2{long long from,to,cost;};

//MODint
template<long long MOD> struct Fp {
    long long val;
    constexpr Fp(long long v = 0) noexcept : val(v % MOD) {
        if (val < 0) val += MOD;
    }
    constexpr long long getmod() { return MOD; }
    constexpr Fp operator - () const noexcept {
        return val ? MOD - val : 0;
    }
    constexpr Fp operator + (const Fp& r) const noexcept { return Fp(*this) += r; }
    constexpr Fp operator - (const Fp& r) const noexcept { return Fp(*this) -= r; }
    constexpr Fp operator * (const Fp& r) const noexcept { return Fp(*this) *= r; }
    constexpr Fp operator / (const Fp& r) const noexcept { return Fp(*this) /= r; }
    constexpr Fp& operator += (const Fp& r) noexcept {
        val += r.val;
        if (val >= MOD) val -= MOD;
        return *this;
    }
    constexpr Fp& operator -= (const Fp& r) noexcept {
        val -= r.val;
        if (val < 0) val += MOD;
        return *this;
    }
    constexpr Fp& operator *= (const Fp& r) noexcept {
        val = val * r.val % MOD;
        return *this;
    }
    constexpr Fp& operator /= (const Fp& r) noexcept {
        long long a = r.val, b = MOD, u = 1, v = 0;
        while (b) {
            long long t = a / b;
            a -= t * b; swap(a, b);
            u -= t * v; swap(u, v);
        }
        val = val * u % MOD;
        if (val < 0) val += MOD;
        return *this;
    }
    constexpr bool operator == (const Fp& r) const noexcept {
        return this->val == r.val;
    }
    constexpr bool operator != (const Fp& r) const noexcept {
        return this->val != r.val;
    }
    friend constexpr ostream& operator << (ostream &os, const Fp<MOD>& x) noexcept {
        return os << x.val;
    }

    friend constexpr istream& operator >> (istream &is, Fp<MOD>& x){
        long long t;
        is >> t;
        x=t;
        return (is);
    }
};
using mint = Fp<MOD1>;

template<typename t>
constexpr t nCr(t n,int r){
    if(r==0)return 1;
    if(n==0)return 0;
    t x=1;
    for(int i=1;i<=r;i++){
        x*=n-i+1;
        x/=i;
    }
    return x;
}

signed main(){
    ios::sync_with_stdio(false);
    cin.tie(nullptr);
    int n,m;
    cin>>n>>m;
    if(abs(n-m)>1)cout<<0<<endl;
    else{
        if(n>m)swap(n,m);
        if(m-n==0){
            mint a=1;
            rep(i,m)a*=i+1;
            rep(i,n)a*=i+1;
            a*=2;
            cout<<a<<endl;
        }else{
            mint a=1;
            rep(i,m)a*=i+1;
            rep(i,n)a*=i+1;
            cout<<a<<endl;
        }
    }
}

Measured memory_bytes: 3636