#include <algorithm>
#include <array>
#include <cassert>
#include <climits>
#include <cmath>
#include <cstdio>
#include <cstring>
#include <deque>
#include <functional>
#include <iomanip>
#include <iostream>
#include <map>
#include <numeric>
#include <queue>
#include <set>
#include <sstream>
#include <stack>
#include <string>
#include <vector>
using namespace std;
typedef long long ll;
#define REP(i,n) for(int i = 0; i < (int)(n); ++i)
#define FOR(i,a,b) for(int i = (a); i < (int)(b); ++i)
#define ALL(c) (c).begin(), (c).end()
#define SIZE(v) ((int)v.size())
template<class T> inline bool chmin(T& a, T b) {
    if (a > b) {
        a = b; return true;
    }
    return false;
}
template<class T> inline bool chmax(T& a, T b) {
    if (a < b) {
        a = b; return true;
    }
    return false;
}
template<int MOD> struct Fp {
    ll val;
    constexpr Fp(ll v = 0) noexcept : val(v % MOD) {
        if (val < 0) val += MOD;
    }
    constexpr int getmod() { return MOD; }
    constexpr Fp operator - () const noexcept {
        return val ? MOD - val : 0;
    }
    constexpr Fp operator + (const Fp& r) const noexcept { return Fp(*this) += r; }
    constexpr Fp operator - (const Fp& r) const noexcept { return Fp(*this) -= r; }
    constexpr Fp operator * (const Fp& r) const noexcept { return Fp(*this) *= r; }
    constexpr Fp operator / (const Fp& r) const noexcept { return Fp(*this) /= r; }
    constexpr Fp& operator += (const Fp& r) noexcept {
        val += r.val;
        if (val >= MOD) val -= MOD;
        return *this;
    }
    constexpr Fp& operator -= (const Fp& r) noexcept {
        val -= r.val;
        if (val < 0) val += MOD;
        return *this;
    }
    constexpr Fp& operator *= (const Fp& r) noexcept {
        val = val * r.val % MOD;
        return *this;
    }
    constexpr Fp& operator /= (const Fp& r) noexcept {
        ll a = r.val, b = MOD, u = 1, v = 0;
        while (b) {
            ll t = a / b;
            a -= t * b; swap(a, b);
            u -= t * v; swap(u, v);
        }
        val = val * u % MOD;
        if (val < 0) val += MOD;
        return *this;
    }
    constexpr bool operator == (const Fp& r) const noexcept {
        return this->val == r.val;
    }
    constexpr bool operator != (const Fp& r) const noexcept {
        return this->val != r.val;
    }
    friend constexpr ostream& operator << (ostream &os, const Fp<MOD>& x) noexcept {
        return os << x.val;
    }
    friend constexpr Fp<MOD> modpow(const Fp<MOD> &a, ll n) noexcept {
        if (n == 0) return 1;
        auto t = modpow(a, n / 2);
        t = t * t;
        if (n & 1) t = t * a;
        return t;
    }
};
constexpr ll MOD = 998244353;
using mint = Fp<MOD>;

#define pb push_back
#define mp make_pair
#define mt make_tuple

// ll solve_slow(ll A, ll B, ll C, ll D) {
//     int y_diff = C - A;
//     int x_diff = D - B;
//     vector<int> shff;
//     REP(y, y_diff) shff.pb(0);
//     REP(x, x_diff) shff.pb(1);

//     do {
//         set<vector<vector<int>>> cells_vec;
//         vector<vector<int>> cells;
//         REP(a, A) {
//             vector<int> line;
//             REP(b, B) {
//                 line.pb(9);
//             }
//             cells.pb(line);
//         }
//         cells_vec.insert(cells);

//         for(auto s: shff) {
//             set<vector<vector<int>>> next_cells_vec;
//             if (s == 0) {
//                 for (auto& cells: cells_vec) {
//                     auto width = SIZE(cells[0]);

//                     REP(w, width) {
//                         vector<vector<int>> next_cells = cells;
//                         vector<int> line;
//                         REP(w2, width) {
//                             if (w == w2) line.pb(1);
//                             else line.pb(0);
//                         }
//                         next_cells.pb(line);
//                         next_cells_vec.insert(next_cells);
//                     }
//                 }
//             }
//             else {
                
//             }
//             cells_vec = 
//         }
     
     
     
//     } while(next_permutation(ALL(shff)));

//     return 777;
// }

vector<pair<mint, mint>> cache(3000 * 3000, mp(0, 0));
vector<int> seen(3000 * 3000);

int to_index(ll C, ll D) {
    --C; --D;
    return C * 3000 + D;
}

pair<mint, mint> solve_fast(ll A, ll B, ll C, ll D) {
    if (seen[to_index(C, D)] != 0) {
        return cache[to_index(C, D)];
    }

    mint ans = 0;
    mint leftnum = 0;

    if (C == A && B == D) {
        ans = 1;
        leftnum = 0;
    }
    // 横に伸ばす
    else if (C == A) {
        auto ret = solve_fast(A, B, C, D - 1);
        ans = ret.first * A;
        leftnum = ans;
    }
    // 縦に伸ばす
    else if (D == B) {
        auto ret = solve_fast(A, B, C - 1, D);
        ans = ret.first * B;
        leftnum = ret.first;  // ?
    }
    else {
        // 横に伸ばす
        auto ret1 = solve_fast(A, B, C, D - 1);
        // 縦に伸ばす
        auto ret2 = solve_fast(A, B, C - 1, D);

        mint ans1 = ret1.first * C; 
        mint ans2 = ret2.first * D;

        ans = ans1 + ans2;
        ans -= ret2.second * (D - 1); // ?
        // cout << "ans = " << ans1 << " + " << ans2
        //      << " - " << ret2.second << " = " << ans << endl;

        leftnum = ans1; // ?
    }

    // cout << "dp(" << A << "," << B << "," << C << "," << D << ") = "
    //      << ans << "," << leftnum << endl;

    cache[to_index(C, D)] = mp(ans, leftnum);
    seen[to_index(C, D)] = 1;

    return mp(ans, leftnum);
}

int main(void)
{
    ios::sync_with_stdio(false);
    cin.tie(0);
    
    // if (1) {
    //     cache.reset(0);

    //     int size = 1000;
    //     // int size = 100;
    //     FOR(a, 1, size) {
    //         FOR(b, 1, size) {
    //             FOR(c, a, size + 1) {
    //                 FOR(d, b, size + 1) {
    //                     auto ret = solve_fast(a, b, c, d);
    //                     cout << a << ", " << b << ", " << c << ", " <<
    //                         d << ": " << ret.first << endl;
    //                     if (ret.first == 0) {
    //                         return 0;
    //                     }
    //                 }
    //             }
    //         }
    //     }
    // }


    ll A, B, C, D;
    cin >> A >> B >> C >> D;

    auto ret = solve_fast(A, B, C, D);
    cout << ret.first << endl;

    return 0;
}


Measured memory_bytes: 179460