#include "bits/stdc++.h"
#pragma GCC optimize("Ofast")

// Begin Header {{{
using namespace std;

#ifndef DEBUG
#define dump(...)
#endif

#define all(x) x.begin(), x.end()
#define rall(x) x.rbegin(), x.rend()
#define rep(i, n) for (intmax_t i = 0, i##_limit = (n); i < i##_limit; ++i)
#define reps(i, b, e) for (intmax_t i = (b), i##_limit = (e); i <= i##_limit; ++i)
#define repr(i, b, e) for (intmax_t i = (b), i##_limit = (e); i >= i##_limit; --i)
#define var(Type, ...) Type __VA_ARGS__; input(__VA_ARGS__)

constexpr size_t operator""_zu(unsigned long long value) { return value; };
constexpr intmax_t operator""_jd(unsigned long long value) { return value; };
constexpr uintmax_t operator""_ju(unsigned long long value) { return value; };

constexpr int INF = 0x3f3f3f3f;
constexpr intmax_t LINF = 0x3f3f3f3f3f3f3f3f_jd;

namespace moke {

    template <class T> using MaxHeap = priority_queue<T, vector<T>, less<T>>;
    template <class T> using MinHeap = priority_queue<T, vector<T>, greater<T>>;

    inline void input() {}
    template <class Head, class... Tail> inline void input(Head&& head, Tail&&... tail) {
        cin >> head;
        input(forward<Tail>(tail)...);
    }

    template <class T> inline void input(vector<T> &vec) {
        for (auto &e: vec) {
            cin >> e;
        }
    }

    template <class T> inline void input(vector<vector<T>> &mat) {
        for (auto &vec: mat) {
            input(vec);
        }
    }

    inline void print() { cout << "\n"; }
    template <class Head, class... Tail> inline void print(Head&& head, Tail&&... tail) {
        static constexpr const char *delim[] = {"", " "};
        cout << head << delim[sizeof...(tail)];
        print(forward<Tail>(tail)...);
    }

    template <class T> inline ostream& operator<<(ostream &strm, const vector<T> &vec) {
        static constexpr const char *delim[] = {" ", ""};
        for (const auto &e: vec) {
            strm << e << delim[&e == &vec.back()];
        }
        return strm;
    }

    template <class T> inline vector<T> make_v(const T &initValue, size_t sz) {
        return vector<T>(sz, initValue);
    }

    template <class T, class... Args> inline auto make_v(const T &initValue, size_t sz, Args... args) {
        return vector<decltype(make_v<T>(initValue, args...))>(sz, make_v<T>(initValue, args...));
    }

    template <class A, class B> inline bool chmax(A &a, const B &b) noexcept {
        return b > a && (a = b, true);
    }

    template <class A, class B> inline bool chmin(A &a, const B &b) noexcept {
        return b < a && (a = b, true);
    }

    template <class A, class B> inline common_type_t<A, B> min(const A &a, const B &b) noexcept {
        return a < b ? a : b;
    }

    template <class A, class B, class... Args> inline common_type_t<A, B, Args...> min(const A &a, const B &b, const Args&... args) noexcept {
        return moke::min(a < b ? a : b, args...);
    }

    template <class A, class B> inline common_type_t<A, B> max(const A &a, const B &b) noexcept {
        return a > b ? a : b;
    }

    template <class A, class B, class... Args> inline common_type_t<A, B, Args...> max(const A &a, const B &b, const Args&... args) noexcept {
        return moke::max(a > b ? a : b, args...);
    }

    template <class A, class B> inline common_type_t<A, B> diff(const A &a, const B &b) noexcept {
        return a < b ? b - a : a - b;
    }

} // namespace moke

// }}} End Header

namespace moke {

constexpr int MOD = int(1e9) + 7;

// Mint {{{
template <int_fast64_t MOD>
class ModInt {
    int_fast64_t value;
public:
    inline ModInt(const ModInt& other) noexcept : value(other.value) {}
    inline ModInt(int_fast64_t value = 0) noexcept :
        value((value >= MOD) ? value % MOD : (value < 0) ? (value + MOD) % MOD : value) {}

    inline ModInt inv() const noexcept { return power(value, MOD - 2); }

    inline ModInt& operator+=(const ModInt& other) noexcept {
        value = (value + other.value) % MOD; return *this;
    }
    inline ModInt& operator-=(const ModInt& other) noexcept {
        value = (MOD + value - other.value) % MOD; return *this;
    }
    inline ModInt& operator*=(const ModInt& other) noexcept {
        value = (value * other.value) % MOD; return *this;
    }
    inline ModInt& operator/=(const ModInt& other) noexcept {
        value = (value * other.inv().value) % MOD; return *this;
    }

    inline ModInt operator+(const ModInt& other) noexcept { return ModInt(*this) += other; }
    inline ModInt operator-(const ModInt& other) noexcept { return ModInt(*this) -= other; }
    inline ModInt operator*(const ModInt& other) noexcept { return ModInt(*this) *= other; }
    inline ModInt operator/(const ModInt& other) noexcept { return ModInt(*this) /= other; }

    inline bool operator==(const ModInt& other) noexcept { return value == *other; }
    inline bool operator!=(const ModInt& other) noexcept { return value != *other; }

    template <class int_>
        explicit inline operator int_() const noexcept { return static_cast<int_>(value); }

    friend ostream& operator<<(ostream &os, ModInt other) noexcept {
        os << other.value; return os;
    }

    friend istream& operator>>(istream &is, ModInt& other) noexcept {
        is >> other.value; return is;
    }

    static constexpr inline ModInt power(int_fast64_t n, int_fast64_t p) noexcept {
        int_fast64_t ret = 1;
        for (; p > 0; p >>= 1) {
            if (p & 1) ret = (ret * n) % MOD;
            n = (n * n) % MOD;
        }
        return ret;
    }
};

using Mint = ModInt<MOD>;
// }}}

// Factorial {{{
#ifdef DEBUG
#define constexpr
#endif

template <size_t N, int M>
struct Factorial {
    uint_fast64_t fact_[N + 1];

    constexpr inline Factorial() : fact_{1} {
        for (size_t i = 1; i <= N; ++i) fact_[i] = (fact_[i - 1] * i) % M;
    }

    constexpr inline Mint operator[] (size_t pos) const { return fact_[pos]; }
};

template <size_t N, int M>
struct InvFact {
    uint_fast64_t inv_[N + 1];
    uint_fast64_t finv_[N + 1];

    constexpr inline InvFact() : inv_{0, 1}, finv_{1, 1} {
        for (size_t i = 2; i <= N; ++i) {
            inv_[i] = M - inv_[M % i] * (M / i) % M;
            finv_[i] = finv_[i - 1] * inv_[i] % M;
        }
    }

    constexpr inline Mint operator[] (size_t pos) const { return finv_[pos]; }
};

#ifdef constexpr
#undef constexpr
#endif

Factorial<510000, MOD> fact;
InvFact<510000, MOD> finv;

Mint nCr(int n, int r) {
    if (n < r) return 0;
    if (n < 0 || r < 0) return 0;
    return fact[n] * (finv[r] * finv[n - r]);
}

Mint nPr(int n, int r) {
    if (n < r) return 0;
    if (n < 0 || r < 0) return 0;
    return fact[n] * finv[r];
}
// }}}

    int main_() {
        ios_base::sync_with_stdio(false);
        cin.tie(nullptr);

        var(intmax_t, N, M);

        if (diff(N, M) >= 2) {
            print(0);
        } else if (N == M) {
            print(fact[N] * fact[M] * 2);
        } else if (diff(N, M) == 1) {
            print(fact[N] * fact[M]);
        }

        return 0;
    }

} // namespace moke

// {{{
signed main() {
    moke::main_();
    return 0;
}
// }}}


Measured memory_bytes: 384