#ifdef LOCAL
#define _GLIBCXX_DEBUG
#endif
#include<bits/stdc++.h>
using namespace std;
#define rep(i,s,t) for(ll i = (ll)(s); i < (ll)(t); i++)
#define rrep(i,s,t) for(ll i = (ll)(s-1);(ll)(t) <= i; i--)
#define all(x) (x).begin(), (x).end()
typedef long long ll;
typedef long double ld;
typedef pair<ll,ll> Pll;
typedef vector<ll> vl;
typedef vector<vl> vvl;
typedef vector<vvl> vvvl;
constexpr ll INF = numeric_limits<ll>::max()/4;
constexpr ll n_max = 2e5+10;
#define int ll

template <typename A, typename B>
string to_string(pair<A, B> p);
string to_string(const string &s) {return '"' + s + '"';}
string to_string(const char *c) {return to_string((string) c);}
string to_string(bool b) {return (b ? "true" : "false");}
template <size_t N>
string to_string(bitset<N> v){
    string res = "";
    for(size_t i = 0; i < N; i++) res += static_cast<char>('0' + v[i]);
    return res;
}
template <typename A>
string to_string(A v) {
    bool first = true;
    string res = "{";
    for(const auto &x : v) {
        if(!first) res += ", ";
        first = false;
        res += to_string(x);
    }
    res += "}";
    return res;
}
template <typename A, typename B>
string to_string(pair<A, B> p){return "(" + to_string(p.first) + ", " + to_string(p.second) + ")";}

void debug_out() {cerr << endl;}
template<typename Head, typename... Tail>
void debug_out(Head H, Tail... T) {
    cerr << " " << to_string(H);
    debug_out(T...);
}

#ifdef LOCAL
#define debug(...) cerr << "[" << #__VA_ARGS__ << "]:", debug_out(__VA_ARGS__)
#else
#define debug(...) 42
#endif

template<class T>
bool chmax(T &a, T b){if(a < b){a = b; return true;} return false;}
template<class T>
bool chmin(T &a, T b){if(a > b){a = b; return true;} return false;}

template<std::int_fast64_t Modulus>
class modint {
    using i64 = int_fast64_t;

    public:
    i64 a;

    constexpr modint(const i64 x = 0) noexcept {
        this -> a = x % Modulus;
        if(a < 0){
            a += Modulus;
        }
    }
    constexpr int getmod() { return Modulus; }
    constexpr modint operator - () const noexcept {
        return a ? Modulus - a : 0;
    }
    constexpr const i64 &value() const noexcept {return a;}
    constexpr modint operator+(const modint rhs) const noexcept {
        return modint(*this) += rhs;
    }
    constexpr modint operator-(const modint rhs) const noexcept {
        return modint(*this) -= rhs;
    }
    constexpr modint operator*(const modint rhs) const noexcept {
        return modint(*this) *= rhs;
    }
    constexpr modint operator/(const modint rhs) const noexcept {
        return modint(*this) /= rhs;
    }
    constexpr modint &operator+=(const modint rhs) noexcept {
        a += rhs.a;
        if(a >= Modulus) {
            a -= Modulus;
        }
        return *this;
    }
    constexpr modint &operator-=(const modint rhs) noexcept {
        if(a < rhs.a) {
            a += Modulus;
        }
        a -= rhs.a;
        return *this;
    }
    constexpr modint &operator*=(const modint rhs) noexcept {
        a = a * rhs.a % Modulus;
        return *this;
    }
    constexpr modint &operator/=(modint rhs) noexcept {
        i64 a_ = rhs.a, b = Modulus, u = 1, v = 0;
        while(b){
            i64 t = a_/b;
            a_ -= t * b; swap(a_,b);
            u -= t * v; swap(u,v);
        }
        a = a * u % Modulus;
        if(a < 0) a += Modulus;
        return *this;
    }
    
    // 自前実装
    constexpr bool operator==(const modint rhs) noexcept {
        return a == rhs.a;
    }
    constexpr bool operator!=(const modint rhs) noexcept {
        return a != rhs.a;
    }
    constexpr bool operator>(const modint rhs) noexcept {
        return a > rhs.a;
    }
    constexpr bool operator>=(const modint rhs) noexcept {
        return a >= rhs.a;
    }
    constexpr bool operator<(const modint rhs) noexcept {
        return a < rhs.a;
    }
    constexpr bool operator<=(const modint rhs) noexcept {
        return a <= rhs.a;
    }
    constexpr modint& operator++() noexcept {
        return (*this) += modint(1);
    }
    // constexpr modint operator++(int) {
    //     modint tmp(*this);
    //     operator++();
    //     return tmp;
    // }
    constexpr modint& operator--() noexcept {
        return (*this) -= modint(1);
    }
    // constexpr modint operator--(int) {
    //     modint tmp(*this);
    //     operator--();
    //     return tmp;
    // }
    template<typename T>
    friend constexpr modint modpow(const modint &mt, T n) noexcept {
        if(n < 0){
            modint t = (modint(1) / mt);
            return modpow(t, -n);
        }
        modint res = 1, tmp = mt;
        while(n){
            if(n & 1)res *= tmp;
            tmp *= tmp;
            n /= 2;
        }
        return res;
    }

    friend constexpr string to_string(const modint &mt) noexcept {
        return to_string(mt.a);
    }
};

// 標準入出力対応
template<std::int_fast64_t Modulus>
std::ostream &operator<<(std::ostream &out, const modint<Modulus> &m) {
    out << m.a;
    return out;
}
template<std::int_fast64_t Modulus>
std::istream &operator>>(std::istream &in, modint<Modulus> &m) {
    ll a;
    in >> a;
    m = modint<Modulus>(a);
    return in;
}


// const ll MOD = 1e9+7;
const ll MOD = 998244353;
using mint = modint<MOD>;

signed main(){
    cin.tie(nullptr);
    ios::sync_with_stdio(false);
    ll a,b; cin >> a >> b;
    ll c,d; cin >> c >> d;
    vector dp(c+1, vector<mint>(d+1, 0)), dp2(c+1, vector<mint>(d+1)), dp3(c+1, vector<mint>(d+1));
    
    dp[a][b] = 1;
    rep(i,b,d){
        dp[a][i+1] = dp[a][i] * a;
    }
    rep(i,a,c){
        dp[i+1][b] = dp[i][b] * b;
    }
    debug(dp);
    rep(i,a,c)rep(j,b,d){
        dp[i+1][j+1] = dp[i+1][j] * mint(i+1) + dp[i][j+1] * mint(j+1) - dp[i][j] * mint(i * j);
    }
    debug(dp);
    cout << dp[c][d] << endl;
}

Measured memory_bytes: 214660