abc065-C.cpp

#include <bits/stdc++.h>  
 
using namespace std;
 
#define FOR(i, j, k) for(int i = j; i < k; ++i)
#define rep(i, j) FOR(i, 0, j)
#define FORr(i, j, k) for(int i = j; i >= k; --i)
#define repr(i, j) FOR(i, j, 0)
#define INF (1 << 30)
 
typedef long long ll;
typedef unsigned long long ull;
typedef pair<int, int> P;
typedef pair<P, int> Pi;
 
const ll MOD = 1e9 + 7;
const int dy[]={0, 0, 1, -1};
const int dx[]={1, -1, 0, 0};
 
template <class T> void chmin(T& a, const T& b) { a = min(a, b); }
template <class T> void chmax(T& a, const T& b) { a = max(a, b); }
 
ll modnPr(ll n, ll r) {
	int res = 1;
	for(ll i = 0; i < r; ++i) {
		res =  res * (n - i) % MOD;
	}
	return res;
}
 
int main() {
	ll N, M;
	scanf("%lld %lld", &N ,&M);
	if(abs(N - M) > 1) printf("%d\n", 0);
	else {
		if(N == M) {
			ll dog = modnPr(N, N) % MOD;
			ll monkey = modnPr(M, M) % MOD;
			ll ans = dog * monkey * 2 % MOD;
			printf("%lld\n", ans);
		}
		else {
			ll dog = modnPr(N, N) % MOD;
			ll monkey = modnPr(M, M) % MOD;
			ll ans = dog * monkey % MOD;
			printf("%lld\n", ans);
		}
	} 
	return 0;
}