#include <iostream>
#include <sstream>
#include <algorithm>
#include <string>
#include <vector>
#include <map>
#include <set>
#include <queue>
#include <deque>
#include <stack>
#include <memory>
#include <complex>
#include <numeric>
#include <cstdio>
#include <iomanip>
#include <random>

#define REP(i,m,n) for(int i=int(m);i<int(n);i++)
#define RREP(i,m,n) for(int i=int(n)-1;i>=int(m);--i)
#define EACH(i,c) for (auto &(i): c)
#define all(c) begin(c),end(c)
#define EXIST(s,e) ((s).find(e)!=(s).end())
#define SORT(c) sort(begin(c),end(c))
#define pb emplace_back
#define MP make_pair
#define SZ(a) int((a).size())
//#define int long long

#ifdef LOCAL
#define DEBUG(s) cout << (s) << endl
#define dump(x)  cerr << #x << " = " << (x) << endl
#define BR cout << endl;
#else
#define DEBUG(s) do{}while(0)
#define dump(x) do{}while(0)
#define BR 
#endif
using namespace std;

using UI = unsigned int;
using UL = unsigned long;
using LL = long long;
using ULL = unsigned long long;
using VI = vector<int>;
using VVI = vector<VI>;
using VLL = vector<LL>;
using VVLL = vector<VLL>;
using VS = vector<string>;
using PII = pair<int,int>;
using VP = vector<PII>;
template<class T>bool chmax(T &a, const T &b) { if (a<b) { a=b; return 1; } return 0; }
template<class T>bool chmin(T &a, const T &b) { if (b<a) { a=b; return 1; } return 0; }

constexpr int MOD = 998244353;

long long power(long long x, long long n, long long mod = MOD) {
    if (n == 0) return 1;
    if (n % 2 == 0) return power(x * x % mod, n/2, mod);
    else return x * power(x, n-1, mod) % mod;
}

// auto mod int
struct mint {
    LL x;
    mint(LL x=0):x((x%MOD+MOD)%MOD){}
    mint operator-() const { return mint(-x);}
    mint& operator+=(const mint a) {
        if ((x += a.x) >= MOD) x -= MOD;
        return *this;
    }
    mint& operator-=(const mint a) {
        if ((x += MOD-a.x) >= MOD) x -= MOD;
        return *this;
    }
    mint& operator*=(const mint a) {
        (x *= a.x) %= MOD;
        return *this;
    }
    mint operator+(const mint a) const {
        mint res(*this);
        return res+=a;
    }
    mint operator-(const mint a) const {
        mint res(*this);
        return res-=a;
    }
    mint operator*(const mint a) const {
        mint res(*this);
        return res*=a;
    }
    mint pow(const LL &t) const {
        if (!t) return 1;
        mint a = pow(t>>1);
        a *= a;
        if (t&1) a *= *this;
        return a;
    }

    // for prime MOD
    mint inv() const {
        return pow(MOD-2);
    }
    mint& operator/=(const mint a) {
        return (*this) *= a.inv();
    }
    mint operator/(const mint a) const {
        mint res(*this);
        return res/=a;
    }
    LL operator()() const {
        return x;
    }
};
using VM = vector<mint>;
using VVM = vector<VM>;

void solve() {
    int a,b,c,d;
    cin >> a >> b >> c >> d;
    /*
    mint ans = 1;
    ans *= power(a,d-b);
    ans *= power(b,c-a);
    */
    VVM dp(c+1,VM(d+1));
    dp[a][b] = 1;
    REP(i,a+1,c+1) dp[i][b] = dp[i-1][b] * b; 
    REP(i,b+1,d+1) dp[a][i] = dp[a][i-1] * a;
    REP(i,a+1,c+1) {
        REP(j,b+1,d+1) {
            dp[i][j] = dp[i][j-1] * i + dp[i-1][j] * j - dp[i-1][j-1] * (i-1) * (j-1);
        }
    } 

    cout << dp[c][d]() << endl;

    return;

    REP(i,0,c+1) {
        REP(j,0,d+1) {
            cout << dp[i][j]() << " ";
        }
        cout << endl;
    }
}

signed main() {
    solve();
    
    return 0;
}

Measured memory_bytes: 73744