#include <bits/stdc++.h>

using namespace std;
using ll = long long;
using Graph = vector<vector<int>>;
using WGraph = vector<vector<pair<int, ll>>>;

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

constexpr int dx[4] = {-1, 0, 0, 1}, dy[4] = {0, -1, 1, 0};
constexpr int INF = 1e9;
// constexpr int MOD = 1e9 + 7;
constexpr long long LINF = 1e18;
constexpr double EPS = 1e-10;
constexpr double PI = M_PI;

constexpr int MOD = 998244353;

template<int mod>
class ModInt {
    private:
        long long val;
    public:
        constexpr ModInt(const long long v = 0) : val(v%mod) { if (val < 0) val += mod; }
        constexpr ModInt(const ModInt &v) : val(v.val) {}
        constexpr ModInt &operator=(const long long v) { val = v; return *this; }
        constexpr ModInt &operator=(const ModInt &v) { if (this != &v) val = v.val; return *this; }
        constexpr ModInt operator+() const { return ModInt(val); }
        constexpr ModInt operator-() const { return ModInt(-val); }
        constexpr ModInt operator+(const ModInt &v) const { return ModInt(*this) += v; }
        constexpr ModInt operator-(const ModInt &v) const { return ModInt(*this) -= v; }
        constexpr ModInt operator*(const ModInt &v) const { return ModInt(*this) *= v; }
        constexpr ModInt operator/(const ModInt &v) const { return ModInt(*this) /= v; }
        constexpr ModInt &operator+=(const ModInt &v) { val += v.val; if (val >= mod) val -= mod; return *this; }
        constexpr ModInt &operator-=(const ModInt &v) { val -= v.val; if (val < 0) val += mod; return *this; }
        constexpr ModInt &operator*=(const ModInt &v) { val *= v.val; if (val >= mod) val %= mod; return *this; }
        constexpr ModInt &operator/=(const ModInt &v) { val *= v.inverse().val; if (val >= mod) val %= mod; return *this; }
        constexpr ModInt &operator++() { ++val; if (val >= mod) val -= mod; return *this; }
        constexpr ModInt &operator--() { --val; if (val < 0) val += mod; return *this; }
        constexpr ModInt operator++(int) { ModInt tmp(*this); operator++(); return tmp; }
        constexpr ModInt operator--(int) { ModInt tmp(*this); operator--(); return tmp; }
        constexpr bool operator==(const ModInt &v) const { return val == v.val; }
        constexpr bool operator!=(const ModInt &v) const { return !(*this == v); }
        friend std::istream &operator>>(std::istream &s, ModInt &v) { long long tmp; s >> tmp; v = ModInt(tmp); return s; }
        friend std::ostream &operator<<(std::ostream &s, const ModInt &v) { return s << v.val; }
        constexpr ModInt inverse() const {
            long long n = val, res = 1;
            while (n > 1) {
                res *= (mod - mod / n);
                res %= mod;
                n = mod % n;
            }
            return ModInt(res);
        }
        static constexpr ModInt modpow(ModInt v, long long n) {
            ModInt res(1);
            for ( ; n>0; n>>=1) {
                if (n & 1) res *= v;
                v *= v;
            }
            return res;
        }
};

using MInt = ModInt<MOD>;

void solve() {
    int A, B, C, D;
    cin >> A >> B >> C >> D;

    if (C < A || D < B) {
        cout << 0 << '\n';
        return;
    }

    vector<vector<MInt>> dp0(C+1, vector<MInt>(D+1)), dp1(C+1, vector<MInt>(D+1));
    dp0[A][B] = 1;
    for (int i=A+1; i<C+1; ++i) dp0[i][B] = dp0[i-1][B] * B;
    for (int i=B+1; i<D+1; ++i) dp0[A][i] = dp0[A][i-1] * A;
    for (int i=A+1; i<C+1; ++i) {
        for (int j=B+1; j<D+1; ++j) {
            dp0[i][j] = (dp0[i-1][j] + dp1[i-1][j]) * j;
            dp1[i][j] = dp0[i][j-1] + dp1[i][j-1] * i;
        }
    }
    cout << dp0[C][D] + dp1[C][D] << '\n';
}

int main() {
    ios::sync_with_stdio(false);
    cin.tie(0);
    cout << fixed << setprecision(20);

    solve();

    return 0;
}


Measured memory_bytes: 144096