#include <algorithm>
#include <bitset>
#include <complex>
#include <deque>
#include <exception>
#include <fstream>
#include <functional>
#include <iomanip>
#include <ios>
#include <iosfwd>
#include <iostream>
#include <istream>
#include <iterator>
#include <limits>
#include <list>
#include <locale>
#include <map>
#include <memory>
#include <new>
#include <numeric>
#include <ostream>
#include <queue>
#include <set>
#include <sstream>
#include <stack>
#include <stdexcept>
#include <streambuf>
#include <string>
#include <typeinfo>
#include <utility>
#include <valarray>
#include <vector>
#include <climits>
#include <cstring>
#include <cassert>


using namespace std;
#define SZ(x) (int)(x.size())
#define REP(i, n) for(int i=0;i<n;++i)
#define FOR(i, a, b) for(int i=a;i<b;++i)
#define RREP(i, n) for(int i=n-1;i>=0;--i)
#define RFOR(i, a, b) for(int i=b-1;i>=a;--i)

#define all(x) begin(x),end(x)
#define dump(x) cerr<<#x<<" = "<<(x)<<endl
#define debug(x) cerr<<#x<<" = "<<(x)<<" (L"<<__LINE__<<")"<< endl;

using ll = long long;
using vi = vector<int>;
using vvi = vector<vi>;
using vll = vector<ll>;
using vvll = vector<vll>;
using P = pair<int, int>;
const double eps = 1e-8;
const ll MOD = 998244353;
const int INF = INT_MAX / 2;
const ll LINF = LLONG_MAX / 2;

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

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


template<typename T1, typename T2>
ostream &operator<<(ostream &os, const pair<T1, T2> p) {
    os << p.first << ":" << p.second;
    return os;
}

template<class T>
ostream &operator<<(ostream &os, const vector<T> &v) {
    os << "[";
    REP(i, SZ(v)) {
        if (i) os << ", ";
        os << v[i];
    }
    return os << "]";
}

template<class T1, class T2>
ostream &operator<<(ostream &os, const map<T1, T2> &mp) {
    os << "[";
    for (auto it = mp.begin(); it != mp.end(); ++it) {
        if (it != mp.begin()) {
            os << ", ";
        }
        os << *it;
    }
    return os << "]";
}

class Mint {
    using u64 = std::uint_fast64_t;
    u64 Modulus = MOD;

public:
    u64 a;

    constexpr Mint(const u64 x = 0) noexcept: a(x % Modulus) {}

    constexpr u64 &value() noexcept { return a; }

    constexpr const u64 &value() const noexcept { return a; }

    constexpr Mint operator+(const Mint rhs) const noexcept {
        return Mint(*this) += rhs;
    }

    constexpr Mint operator-(const Mint rhs) const noexcept {
        return Mint(*this) -= rhs;
    }

    constexpr Mint operator*(const Mint rhs) const noexcept {
        return Mint(*this) *= rhs;
    }

    constexpr Mint operator/(const Mint rhs) const noexcept {
        return Mint(*this) /= rhs;
    }

    constexpr Mint &operator+=(const Mint rhs) noexcept {
        a += rhs.a;
        if (a >= Modulus) {
            a -= Modulus;
        }
        return *this;
    }

    constexpr Mint &operator-=(const Mint rhs) noexcept {
        if (a < rhs.a) {
            a += Modulus;
        }
        a -= rhs.a;
        return *this;
    }

    constexpr Mint &operator*=(const Mint rhs) noexcept {
        a = a * rhs.a % Modulus;
        return *this;
    }

    constexpr Mint &operator/=(Mint rhs) noexcept {
        u64 exp = Modulus - 2;
        while (exp) {
            if (exp % 2) {
                *this *= rhs;
            }
            rhs *= rhs;
            exp /= 2;
        }
        return *this;
    }

    constexpr Mint &pow(int rhs) noexcept {
        u64 exp = static_cast<u64>(rhs);
        Mint base(a);
        a = 1;
        while (exp) {
            if (exp % 2) {
                *this *= base;
            }
            base *= base;
            exp /= 2;
        }
        return *this;
    }

};

// edit
const int LIM = 31;
//bool check[LIM][LIM];
//Mint dp[LIM][LIM];

void solve() {
    ll A, B, C, D;
    cin >> A >> B >> C >> D;
    vector<vector<Mint>> dp(C + 2, vector<Mint>(D + 2));
    dp[A][B] = 1;

    Mint div2 = Mint(1) / Mint(2);

    for (int h = A; h <= C; ++h) {
//        if (h == A) {
//            for (int w = B; w <= D; ++w) {
//                dp[h][w + 1] += dp[h][w] * h;
//                dp[h + 1][w] += dp[h][w] * h;
//            }
//            continue;
//        }
        for (int w = B; w <= D; ++w) {
            if (h > A && w > B) {
                dp[h][w] -= dp[h - 1][w - 1] * (h - 1) * (w - 1);
            }
            dp[h + 1][w] += dp[h][w] * w;
            dp[h][w + 1] += dp[h][w] * h;
//            if (w == B) {
//                dp[h + 1][w] += dp[h][w] * w;
//                dp[h + 1][w] += dp[h][w] * w;
//                continue;
//            }


//            if (h > A) {
//                dp[h][w + 1] += dp[h][w] * (h + 1) * div2;
//            } else {
//                dp[h][w + 1] += dp[h][w] * h;
//            }
//
//            if (w > B) {
//                dp[h + 1][w] += dp[h][w] * (w + 1) * div2;
//            } else {
//                dp[h + 1][w] += dp[h][w] * w;
//            }
        }
    }

    Mint ans = dp[C][D];

    cout << ans.value() << endl;
}


int main() {
    cin.tie(0);
    ios::sync_with_stdio(false);
    cout << fixed << setprecision(10);
//    std::ifstream in("input.txt");
//    std::cin.rdbuf(in.rdbuf());

    solve();


    return 0;
}


Measured memory_bytes: 143936