#include <bits/stdc++.h>

using namespace std;

#define REP(i, n) for (int i=0; i<(n); ++i)
#define RREP(i, n) for (int i=(int)(n)-1; i>=0; --i)
#define FOR(i, a, n) for (int i=(a); i<(n); ++i)
#define RFOR(i, a, n) for (int i=(int)(n)-1; i>=(a); --i)

#define SZ(x) ((int)(x).size())
#define ALL(x) (x).begin(),(x).end()

#define DUMP(x) cerr<<#x<<" = "<<(x)<<endl
#define DEBUG(x) cerr<<#x<<" = "<<(x)<<" (L"<<__LINE__<<")"<<endl;

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 T, class U>
ostream &operator<<(ostream &os, const pair <T, U> &p) {
    return os << "(" << p.first << " " << p.second << ")";
}

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;
}

using ll = long long;
using ull = unsigned long long;
using ld = long double;
using P = pair<int, int>;
using vi = vector<int>;
using vll = vector<ll>;
using vvi = vector<vi>;
using vvll = vector<vll>;

const ll MOD = 1e9 + 7;
const int INF = INT_MAX / 2;
const ll LINF = LLONG_MAX / 2;
const ld eps = 1e-9;

int gcd(int a, int b) {
    if (a == 0) return b;
    return gcd(b % a, a);
}

template<int64_t mod>
class modint {
    int64_t x;

public:
    modint(int64_t x = 0) : x(x < 0 ? ((x % mod) + mod) % mod : x % mod) {}

    const modint operator-() const { return x == 0 ? 0 : mod - x; }

    modint& operator+=(const modint& rhs) {
        if ((x += rhs.x) >= mod) x -= mod;
        return *this;
    }
    modint& operator-=(const modint& rhs) {
        return *this += -rhs;
    }
    modint& operator*=(const modint& rhs) {
        (x *= rhs.x) %= mod;
        return *this;
    }
    modint& operator/=(const modint& rhs) {
        return *this *= rhs.pow(mod - 2);
    }

    friend const modint operator+(modint lhs, const modint& rhs) {
        return lhs += rhs;
    }
    friend const modint operator-(modint lhs, const modint& rhs) {
        return lhs -= rhs;
    }
    friend const modint operator*(modint lhs, const modint& rhs) {
        return lhs *= rhs;
    }
    friend const modint operator/(modint lhs, const modint& rhs) {
        return lhs /= rhs;
    }

    const modint pow(int64_t n) const {
        modint ret = 1, tmp = *this;
        while (n) {
            if (n & 1) ret *= tmp;
            tmp *= tmp; n >>= 1;
        }
        return ret;
    }

    friend bool operator==(const modint& lhs, const modint& rhs) {
        return lhs.x == rhs.x;
    }
    friend bool operator!=(const modint& lhs, const modint& rhs) {
        return lhs.x != rhs.x;
    }

    friend ostream& operator<<(ostream& os, const modint& a) {
        return os << a.x;
    }
    friend istream& operator>>(istream& is, modint& a) {
        int64_t tmp; is >> tmp; a = tmp;
        return is;
    }
};

int main() {
    cin.tie(0);
    ios::sync_with_stdio(false);
    cout << fixed << setprecision(10);

    // ifstream in("in.txt");
    // cin.rdbuf(in.rdbuf());

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

    using Int = modint<998244353>;

    vector<vector<Int>> dp(C+1, vector<Int>(D+1));

    dp[A][B] = 1;
    for (int i = A; i <= C; ++i) {
        for (int j = B; j <= D; ++j) {
            if (i > A) {
                dp[i][j] += dp[i-1][j] * j;
            }
            if (j > B) {
                dp[i][j] += dp[i][j-1] * i;
            }
            if (i > A and j > B) {
                dp[i][j] -= dp[i-1][j-1] * (i-1) * (j-1);
            }
        }
    }

    cout << dp[C][D] << endl;

    return 0;
}


Measured memory_bytes: 73680