065_C.cpp

#include<bits/stdc++.h>
using namespace std;
#define ll long long
const ll mod=1000000007;

ll facctoria(ll k){
  ll mol=1;
  for (ll i=1;i<=k;++i)
  {
    mol*=i;
    mol%=mod;
}
  return mol;
}
int main(){
  ll n,m;cin>>n>>m;
  ll N=facctoria(n)%mod;
  ll M=facctoria(m)%mod;
  if(abs(n-m)==0){
    cout<<(2*N*M)%mod<<endl;
    }else if(abs(n-m)==1){
      cout<<(N*M)%mod<<endl;
    }else{
      cout<<0<<endl;
  }
}