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#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;
}
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