#include<bits/stdc++.h>
using namespace std;
typedef long long ll;
typedef long double ld;
typedef pair<ll,ll> P;
typedef pair<int,int> Pi;
#define rep(i,n) for(ll i=0;i<n;i++)
#define FOR(i,a,b) for(ll i=a;i<b;i++)
#define fi first
#define se second
#define endl "\n"

template<typename T> inline bool chmax(T &a, T b){if(a<b){a=b;return true;}return false;}
template<typename T> inline bool chmin(T &a, T b){if(a>b){a=b;return true;}return false;}
template<typename T> ostream& operator<<(ostream& s,const complex<T>& d) {return s<<"("<<d.real()<<", "<<d.imag()<< ")";}
template<typename T1, typename T2> ostream& operator<<(ostream& s,const pair<T1,T2>& d) {return s<<"("<<d.first<<", "<<d.second<<")";}
template<typename T> ostream& operator<<(ostream& s, const vector<T>& d){int len=d.size();rep(i,len){s<<d[i];if(i<len-1) s<<" ";}return s;}
template<typename T> ostream& operator<<(ostream& s,const vector<vector<T>>& d){int len=d.size();rep(i,len){s<<d[i]<<endl;}return s;}
template<typename T> ostream& operator<<(ostream& s,const set<T>& v){s<<"{ ";for(auto itr=v.begin();itr!=v.end();++itr) {if (itr!=v.begin()) {s<< ", ";}s<<(*itr);}s<<" }";return s;}
template<typename T> ostream& operator<<(ostream& s,const multiset<T>& v){s<<"{ ";for(auto itr=v.begin();itr!=v.end();++itr) {if (itr!=v.begin()) {s<< ", ";}s<<(*itr);}s<<" }";return s;}
template<typename T1, typename T2> ostream& operator<<(ostream& s,const map<T1,T2>& m){s<<"{"<<endl;for(auto itr=m.begin();itr!=m.end();++itr){s<<" "<<(*itr).first<<" : "<<(*itr).second<<endl;}s<<"}"<<endl;return s;}

const ll mod=1e9+7;
const ll inf=1e17;
const int INF=1e9;
const double EPS=1e-10;
const double PI=acos(-1);

struct mint{
    ll x;
    mint(ll x=0):x((x%mod+mod)%mod){}
    friend ostream &operator<<(ostream& os,const mint& a){
        return os<<a.x;
    }
    friend istream &operator>>(istream& is,mint& a){
        ll t;
        is>>t;
        a=mint(t);
        return (is);
    }
    mint& operator+=(const mint a){
        if((x+=a.x)>=mod) x-=mod;
        return *this;
    }
    mint& operator-=(const mint a){
        if((x+=mod-a.x)>=mod)x-=mod;
        return *this;
    }
    mint& operator*=(const mint a){
        (x*=a.x)%=mod;
        return *this;
    }
    mint operator+(const mint a) const{
        mint res(*this);
        return res+=a;
    }
    mint operator-(const mint a) const{
        mint res(*this);
        return res-=a;
    }
    mint operator*(const mint a) const{
        mint res(*this);
        return res*=a;
    }
    mint pow(ll t) const{
        if (!t) return 1;
        mint a=pow(t>>1);
        a*=a;
        if(t&1) a*=*this;
        return a;
    }
    // for prime mod
    mint inv() const{
        return pow(mod-2);
    }
    mint& operator/=(const mint a){
        return (*this)*=a.inv();
    }
    mint operator/(const mint a) const{
        mint res(*this);
        return res/=a;
    }
};

struct combination{
  vector<mint> fact,ifact;
  combination(int n):fact(n+1),ifact(n+1){
    assert(n<mod);
    fact[0]=1;
    for(int i=1;i<=n;i++) fact[i]=fact[i-1]*i;
    ifact[n]=fact[n].inv();
    for(int i=n;i>=1;i--) ifact[i-1]=ifact[i]*i;
  }
  mint operator()(int n,int k){
    if (k<0 || k>n) return 0;
    return fact[n]*ifact[k]*ifact[n-k];
  }
};

int main(){
    cin.tie(0);ios::sync_with_stdio(false);
    int n,m;
    cin>>n>>m;
    if(n>m) swap(n,m);
    combination comb(2*m);
    if(m-n>=2){
        cout<<0<<endl;
    }else if(m-n==1){
        cout<<comb.fact[m]*comb.fact[m-1]<<endl;
    }else{
        cout<<comb.fact[n]*comb.fact[m]*2<<endl;
    }
}

Measured memory_bytes: 3328