#include <bits/stdc++.h>
using namespace std;
constexpr int64_t mod = 998244353;

template <uint32_t mod>
class modint{
    uint64_t value;
public:
    constexpr modint(const int64_t x=0) noexcept: value(x % mod + (x < 0 ? mod : 0)){ }
    constexpr explicit operator uint64_t() const noexcept{ return value; }
    constexpr modint inverse() const noexcept{ return pow(*this, mod-2); }
    constexpr bool operator==(const modint &rhs) const noexcept{ return value == rhs.value; }
    constexpr bool operator!=(const modint &rhs) const noexcept{ return value != rhs.value; }
    constexpr modint operator+() const noexcept{ return modint(*this); }
    constexpr modint operator-() const noexcept{ return modint(mod - value); }
    constexpr modint operator+(const modint &rhs) const noexcept{ return modint(*this) += rhs; }
    constexpr modint operator-(const modint &rhs) const noexcept{ return modint(*this) -= rhs; }
    constexpr modint operator*(const modint &rhs) const noexcept{ return modint(*this) *= rhs; }
    constexpr modint operator/(const modint &rhs) const noexcept{ return modint(*this) /= rhs; }
    constexpr modint &operator+=(const modint &rhs) noexcept{
        if((value += rhs.value) >= mod) value -= mod;
        return *this;
    }
    constexpr modint &operator-=(const modint &rhs) noexcept{ return *this += mod - rhs.value; }
    constexpr modint &operator*=(const modint &rhs) noexcept{
        if((value *= rhs.value) >= mod) value %= mod;
        return *this;
    }
    constexpr modint &operator/=(const modint &rhs) noexcept{ return *this *= rhs.inverse(); }
    constexpr modint operator++(int) noexcept{
        modint ret(*this);
        if((++value) >= mod) value -= mod;
        return ret;
    }
    constexpr modint operator--(int) noexcept{
        modint ret(*this);
        if((value += mod - 1) >= mod) value -= mod;
        return ret;
    }
    constexpr modint &operator++() noexcept{ return *this += 1; }
    constexpr modint &operator--() noexcept{ return *this -= 1; }
    friend std::ostream &operator<<(std::ostream &os, const modint<mod> &x){ return os << x.value; }
    friend std::istream &operator>>(std::istream &is, modint<mod> &x){
        int64_t i;
        is >> i;
        x = modint<mod>(i);
        return is;
    }
    friend constexpr modint<mod> pow(const modint<mod> &x, uint64_t y){
        modint<mod> ret{1}, m{x};
        while(y > 0){
            if(y & 1) ret *= m;
            m *= m;
            y >>= 1;
        }
        return ret;
    }
};

int main(){
    cin.tie(nullptr);
    ios::sync_with_stdio(false);
    
    int a, b, c, d;
    cin >> a >> b >> c >> d;

    static modint<mod> dp[3][3001][3001];
    dp[0][a][b] = 1;
    for(int i=a+1;i<=c;++i){ dp[2][i][b] = 0; dp[0][i][b] = dp[1][i][b] = dp[0][i-1][b] * b; }
    for(int j=b+1;j<=d;++j){ dp[1][a][j] = 0; dp[0][a][j] = dp[2][a][j] = dp[0][a][j-1] * a; }
    
    for(int i=a+1;i<=c;++i){
        for(int j=b+1;j<=d;++j){
            dp[1][i][j] = dp[0][i-1][j] * j;
            dp[2][i][j] = dp[0][i][j-1] * i;
            dp[0][i][j] = dp[1][i][j] + dp[2][i][j] - dp[0][i-1][j-1]*(i-1)*(j-1);
        }
    }
    cout << dp[0][c][d] << endl;
    return 0;
}

Measured memory_bytes: 214616