#pragma GCC optimize("Ofast")

#include <bits/stdc++.h>
#include <ext/pb_ds/tree_policy.hpp>
#include <ext/pb_ds/assoc_container.hpp>
#include <random>

using namespace std;
using namespace __gnu_pbds;

typedef
tree<pair<int, int>, null_type, less<pair<int, int>>, rb_tree_tag, tree_order_statistics_node_update> orderedSet;

#define pb push_back
#define F first
#define S second
#define all(a) (a).begin(), (a).end()

#define for1(i0, l0, r0) for (int i0 = l0; i0 < r0; ++i0)
#define for2(i0, l0, r0) for (int i0 = l0; i0 <= r0; ++i0)
#define forn(i0, n0) for (int i0 = 0; i0 < n0; ++i0)
#define forn1(i0, n0) for (int i0 = 1; i0 < n0; ++i0)
#define forr(i0, n0) for (int i0 = n0; i0 >= 0; --i0)
#define forr1(i0, r0, l0) for (int i0 = r0; i0 > l0; --i0)
#define forr2(i0, r0, l0) for (int i0 = r0; i0 >= l0; --i0)

#define Sort(a) sort(all(a))
#define Reverse(a) reverse(all(a))
#define relaxMax(a, b) a = max(a, b)
#define relaxMin(a, b) a = min(a, b)

typedef long long ll;
typedef long double ld;
#define ui unsigned int
#define ull unsigned long long

typedef pair<int, int> pii;
typedef pair<ll, ll> pll;
typedef pair<double, double> pdd;
typedef pair<string, string> pss;

typedef vector<int> vi;
typedef vector<ll> vll;
typedef vector<double> vd;
typedef vector<ld> vld;
typedef vector<bool> vb;
typedef vector<string> vs;

typedef vector<pii> vpii;
typedef vector<pll> vpll;
typedef vector<pdd> vpdd;

typedef vector<vi> vvi;
typedef vector<vd> vvd;
typedef vector<vll> vvll;
typedef vector<vb> vvb;

#define vpss vector<pss>
#define vvs vector<vs>
#define vvpii vector<vpii>
#define vvpll vector<vpll>
#define vpt vector<pt>
#define vvvi vector<vvi>
#define vsi vector<set<int>>
#define ss second
#define ff first

#define printvi(arr) for (int x0 : arr) cout << x0 << ' '; cout << '\n';
#define printvll(arr) for (ll x0 : arr) cout << x0 << ' '; cout << '\n';
#define printpair(pair0) cout << pair0.F << ' ' << pair0.S << '\n';
#define printvp(arr) for (auto pair0 : arr) printpair(pair0);
#define initArray(arr, N0, X0) memset(arr, X0, N0 * sizeof(int))
//mt19937 rng(chrono::steady_clock::now().time_since_epoch().count());

void init() {
    ios_base::sync_with_stdio(0);
    cin.tie(0);
    cout.tie(0);
    //cout.precision(16);
    //freopen("amusing.in", "r", stdin);
    //freopen("amusing.out", "w", stdout);
}

const ll mod = 998244353;

set<vvi> s;

void go(int a, int b, int c, int d, vvi A){
    if (a == c && b == d){
        s.insert(A);
        return;
    }
    if (a < c){
        forn(j, b){
            vvi B = A;
            B[a + 1][j] = 1;
            go(a + 1, b, c, d, B);
        }
    }
    if (b < d) {
        forn(i, a) {
            vvi B = A;
            B[i][b + 1] = 1;
            go(a, b + 1, c, d, B);
        }
    }
}

void solve() {
    int a, b, c, d;
    cin >> a >> b >> c >> d;
    vvll dp(c + 1, vll(d + 1));
    dp[a][b] = 1;
    for2(i, a, c){
        for2(j, b, d){
            if (i == a && j == b) continue;
            if (i == a)
                dp[i][j] = (a * dp[i][j - 1]) % mod;
            else if (j == b)
                    dp[i][j] = (b * dp[i - 1][j]) % mod;
            else {
                dp[i][j] = (i * dp[i][j - 1] + j * dp[i - 1][j]) % mod;
                dp[i][j] += mod;
                ll x = (((i - 1) * (j - 1)) * dp[i - 1][j - 1]) % mod;
                dp[i][j] -= x;
                dp[i][j] %= mod;
            }
        }
    }
    cout << dp[c][d] << '\n';
}

bool multitest = false;

int main() {
    init();
    int t = 1;
    if (multitest) cin >> t;
    forn(i, t) solve();
}

Measured memory_bytes: 73672