#include <bits/stdc++.h>
#include <iomanip>
using namespace std;
#define reps(i,s,n) for(int i = s; i < n; i++)
#define rep(i,n) reps(i,0,n)
#define Rreps(i,n,e) for(int i = n - 1; i >= e; --i)
#define Rrep(i,n) Rreps(i,n,0)
#define ALL(a) a.begin(), a.end()
#define fi first
#define se second
typedef long long ll;
typedef vector<ll> vec;
typedef vector<vec> mat;

ll N,M,H,W,Q,K,A,B;
string S;
const ll MOD = 998244353;
//const ll MOD = (1e+9) + 7;
typedef pair<ll, ll> P;
const ll INF = (1LL<<58);

class mint{
    public:
        ll x;
        static unsigned long long mod;
        static unsigned long long mod_plus;
        mint(){x = 0;}
        mint(ll _x) : x((_x < 0 ? ((_x += mod_plus) < 0 ? _x + mod_plus : _x) : _x)%mod){}
        /*mint& operator=(const ll &a){
            x = a;
            return *this;
        }*/

        mint operator-(){
            return x == 0 ? 0 : mod - x;
        }
        mint& operator+=(const mint& a){
            if((x += a.x) >= mod) x -= mod;
            return *this;
        }
        mint operator+(const mint& a) const{
            mint res(*this);
            return res += a;
        }
        mint& operator-=(const mint& a){
            if((x -= a.x) < 0) x += mod;
            return *this;
        }
        mint operator-(const mint& a) const{
            mint res(*this);
            return res -= a;
        }
        mint& operator*=(const mint& a){
            (x *= a.x)%=mod;
            return *this;
        }
        /*mint& operator*=(const ll& a){
            mint temp(a);
            return *this *= temp;
        }*/
        mint operator*(const mint& a) const{
            mint res(*this);
            return res *= a;
        }
        /*mint operator*(const ll& a) const{
            mint res(*this);
            return res *= a;
        }*/
        mint pow(unsigned long long pw) const{
            mint res(1), comp(*this);
            while(pw){
                if(pw&1) res *= comp;
                comp *= comp;
                pw >>= 1;
            }
            return res;
        }
        //以下、modが素数のときのみ
        mint inv() const{
            mint res(*this);
            return res.pow(mod - 2);
        }
        mint& operator/=(const mint &a){
            (x *= a.inv().x)%=mod;
            return *this;
        }
        mint operator/(const mint &a) const{
            mint res(*this);
            return res /= a;
        }
};
ostream& operator<<(ostream& os, const mint& a){
    os << a.x;
    return os;
}
unsigned long long mint::mod = 998244353;
unsigned long long mint::mod_plus = (LLONG_MAX / mint::mod) * mint::mod;
typedef vector<mint> vm;

const ll MAX_N = ll(1e+7);
vm fact(MAX_N, mint(1));
void makefact(){
    reps(i,2,MAX_N) fact[i] = fact[i-1] * mint(i);
}
mint nCm(ll n, ll m){
    if(n < m) return 0;
    return fact[n] / (fact[n-m] * fact[m]);
}

int main() {
    vec h(2), w(2);
    rep(i,2) cin>>h[i]>>w[i];
    ll dh = h[1] - h[0], dw = w[1] - w[0];
    /*
    makefact();
    mint res(0);
    rep(i,dh + 1){
        rep(j, dw + 1){
            res += nCm((h[0] + i) * (w[0] + j) - h[0] * w[0], dh + dw) * nCm(dh, i) * nCm(dw, j) * ((dh + dw - i - j)&1 ? -1 : 1);
        }
    }
    cout<<res<<endl;
     */
    vector<vm> dp(dh + 1, vm(dw + 1, 0));
    dp[0][0] = 1;
    rep(i,dh + 1){
        rep(j, dw + 1){
            if(i > 0) dp[i][j] += dp[i-1][j] * (w[0] + j);
            if(j > 0) dp[i][j] += dp[i][j-1] * (h[0] + i);
            if(i > 0 && j > 0) dp[i][j] -= dp[i-1][j-1] * (h[0] + i - 1) * (w[0] + j - 1);
        }
    }
    cout<<dp[dh][dw]<<endl;
}

Measured memory_bytes: 151660