#include <string>
#include <vector>
#include<iostream>
#include<cstdio>
#include<cstdlib>
#include<stack>
#include<queue>
#include<cmath>
#include<algorithm>
#include<functional>
#include<list>
#include<deque>
#include<bitset>
#include<set>
#include<map>
#include<unordered_map>
#include<unordered_set>
#include<cstring>
#include<sstream>
#include<complex>
#include<iomanip>
#include<numeric>
#include<cassert>
#include<random>
#define X first
#define Y second
#define pb push_back
#define rep(X,Y) for (int (X) = 0;(X) < (int)(Y);++(X))
#define reps(X,S,Y) for (int (X) = (int)(S);(X) < (int)(Y);++(X))
#define rrep(X,Y) for (int (X) = (int)(Y)-1;(X) >=0;--(X))
#define rreps(X,S,Y) for (int (X) = (int)(Y)-1;(X) >= (int)(S);--(X))
#define repe(X,Y) for ((X) = 0;(X) < (Y);++(X))
#define peat(X,Y) for (;(X) < (Y);++(X))
#define all(X) (X).begin(),(X).end()
#define rall(X) (X).rbegin(),(X).rend()
#define eb emplace_back
#define UNIQUE(X) (X).erase(unique(all(X)),(X).end())
#define Endl endl
#define NL <<"\n"

using namespace std;
using ll=long long;
using pii=pair<int,int>;
using pll=pair<ll,ll>;
template<class T> using vv=vector<vector<T>>;
template<class T> inline bool MX(T &l,const T &r){return l<r?l=r,1:0;}
template<class T> inline bool MN(T &l,const T &r){return l>r?l=r,1:0;}
//#undef NUIP
#ifdef NUIP
#include "benri.h"
#else
#define out(args...)
#endif
#ifdef __cpp_init_captures
template<typename T>vector<T> table(int n, T v){ return vector<T>(n, v);}
template <class... Args> auto table(int n, Args... args){auto val = table(args...); return vector<decltype(val)>(n, move(val));}
#endif
const ll MOD=998244353;

ll modpow_(ll r,ll n,ll m=MOD){
  ll re=1,d=r%m;
  if(n<0)(n%=m-1)+=m-1;
  for(;n;n/=2){
    if(n&1)(re*=d)%=m;
    (d*=d)%=m;
  }
  return re;
}
template <int mod=MOD> struct ModInt{
  int v;
  ModInt(int v=0):v(v){}
  ModInt operator+(const ModInt &n)const{return v+n.v<mod ? v+n.v : v+n.v-mod;}
  ModInt operator-(const ModInt &n)const{return v-n.v<0 ? v-n.v+mod : v-n.v;}
  ModInt operator*(const ModInt &n)const{return ll(v)*n.v%mod;}
  ModInt operator/(const ModInt &n)const{return ll(v)*modpow_(n.v%mod,-1,mod)%mod;}
  ModInt operator+(const ll &n)const{return v+n<mod ? v+n : v+n-mod;}
  ModInt operator-(const ll &n)const{return v-n<0 ? v-n+mod : v-n;}
  ModInt operator*(const ll &n)const{return ll(v)*(n%mod)%mod;}
  ModInt operator/(const ll &n)const{return ll(v)*modpow_(n%mod,-1,mod)%mod;}
  ModInt& operator+=(const ModInt &n){v+=n.v; if(v>=mod) v-=mod; return *this;}
  ModInt& operator-=(const ModInt &n){v-=n.v; if(v<0) v+=mod; return *this;}
  ModInt& operator*=(const ModInt &n){v=ll(v)*n.v%mod; return *this;}
  ModInt& operator/=(const ModInt &n){v=ll(v)*modpow_(n.v,-1,mod)%mod; return *this;}
  ModInt& operator+=(const ll &n){v+=n; if(v>=mod) v-=mod; return *this;}
  ModInt& operator-=(const ll &n){v-=n; if(v<0) v+=mod; return *this;}
  ModInt& operator*=(const ll &n){v=ll(v)*n%mod; return *this;}
  ModInt& operator/=(const ll &n){v=ll(v)*modpow_(n,-1,mod)%mod; return *this;}
	bool operator==(const ModInt &n)const{return v==n.v;};
	bool operator!=(const ModInt &n)const{return v!=n.v;};
	ModInt& operator++(){ return operator+=(1); }
	ModInt& operator--(){ return operator-=(1); }
	ModInt operator++(int i){ ModInt tmp(*this); operator++(); return tmp; }
	ModInt operator--(int i){ ModInt tmp(*this); operator--(); return tmp; }
};
#ifdef NUIP
class MINT_FRAC____{
public:
	unordered_map<int,pii> dict;
	MINT_FRAC____(int n){
		rep(p,n+1)reps(q,1,n+1)if(__gcd(p,q)==1){
			dict[1ll*p*modpow_(q,-1)%MOD]=pii(p,q);
			dict[MOD-1ll*p*modpow_(q,-1)%MOD]=pii(-p,q);
		}
	}
} Il1Il1Il1(1000);
template<int mod> ostream& operator<<(ostream &os,const ModInt<mod> &n){if(Il1Il1Il1.dict.count(n.v)) os<<n.v<<"("<<Il1Il1Il1.dict[n.v].X<<"/"<<Il1Il1Il1.dict[n.v].Y<<")";else os<<n.v;return os;};
#else
template<int mod> ostream& operator<<(ostream &os,const ModInt<mod> &n){return os<<n.v;};
#endif
template<int mod> ModInt<mod> operator+(const ll &n,const ModInt<mod> &m){return m.v+n<mod ? m.v+n : m.v+n-mod;}
template<int mod> ModInt<mod> operator-(const ll &n,const ModInt<mod> &m){return n-m.v<0 ? n-m.v+mod : n-m.v;}
template<int mod> ModInt<mod> operator*(const ll &n,const ModInt<mod> &m){return ll(m.v)*(n%mod)%mod;}
template<int mod> ModInt<mod> operator/(const ll &n,const ModInt<mod> &m){return ModInt<mod>(n%mod)/m;}
typedef ModInt<MOD> mint;
template <int mod> ModInt<mod> modpow(ModInt<mod> r,ll n){ ModInt<mod> re(1); if(n<0)(n%=mod-1)+=mod-1; for(;n;n/=2){if(n&1) re*=r; r*=r;} return re;}
vector<mint> fact,finv,inv;
mint comb(ll n,ll r){ if(n<r||r<0)return 0; return fact[n]*finv[n-r]*finv[r];}
class Doralion{
  void Modinvs(vector<mint> &re,int n){ re.resize(n+1); re[1]=1; for(int i=2;i<=n;++i)re[i]=re[MOD%i]*(MOD-MOD/i);}
  void Facts(vector<mint> &re,int n){ re.resize(n+1); re[0]=1; rep(i,n)re[i+1]=re[i]*(i+1);}
  void Factinvs(vector<mint> &re,const vector<mint> &inv,int n){ re.resize(n+1); re[0]=1; rep(i,n)re[i+1]=re[i]*inv[i+1];}
public:
  Doralion(int n){ Modinvs(inv,n); Facts(fact,n); Factinvs(finv,inv,n);}
} doralion(1123456);
using pmm=pair<mint,mint>;
mint modpow(ll r,ll n){ return modpow_(r,n);}

mint dp[3123][3123];

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

	int n,m,N,M;
	cin>>n>>m>>N>>M;
	dp[n][m]=1;
	reps(i,n,N){
		mint sum=0;
		reps(j,m,M+1){
			dp[i+1][j]+=dp[i][j]*j+sum;
			(sum+=dp[i][j])*=i;
		}
	}
	// rep(i,N+1){rep(j,M+1) cout<<dp[i][j]<<","; cout NL; }
	mint re=0;
	mint pw=1;
	rrep(j,M+1){
		re+=pw*dp[N][j];
		pw*=N;
	}
	cout<<re NL;
	return 0;
	
	using MP=vector<string>;
	set<MP> st; st.insert({"."});
	queue<MP> que; que.push({"."});
	const int UB=5;
	while(que.size()){
		auto mp=que.front(); que.pop();
		{
			int n=mp.size();
			int m=mp[0].size();
			vector nxt(m,string(n,'.'));
			rep(i,n)rep(j,m) nxt[j][i]=mp[i][j];
			if(st.insert(nxt).Y) que.emplace(nxt);
		}
		{
			int n=mp.size();
			int m=mp[0].size();
			if(n==UB) continue;
			vector nxt=mp;
			nxt.eb(m,'.');
			rep(j,m){
				nxt[n][j]='#';
				if(st.insert(nxt).Y) que.emplace(nxt);
				nxt[n][j]='.';
			}
		}
	}

	int cnt=0;
	for(auto &mp:st){
		if(mp.size()==5 && mp[0].size()==5){
			// rep(i,4) cout<<mp[i] NL;
			// cout NL;
			++cnt;
		}
	}
	out(cnt,1);
  return 0;
}


Measured memory_bytes: 54292