#include <iostream>
using ll = long long;

ll mod_pow( ll a, ll n, ll mod )
{
    ll r = 1;
    while (n > 0) {
        if (n & 1) r = r * a % mod;
        a = a * a % mod;
        n >>= 1;
    }
    return r % mod;
}

ll combination( ll n, ll r, ll mod )
{
    ll x = 1, y = 1;
    for (ll i = 0; i < r; i++) {
        x = x * ( n - i ) % mod;
        y = y * ( i + 1 ) % mod;
    }
    return x * mod_pow( y, mod - 2, mod ) % mod;
}

ll factorial( ll n, ll mod )
{
    ll a = 1;
    for (ll i = 2; i <= n; i++) {
        a = a * i % mod;
    }
    return a;
}

int main( void )
{
    ll X, Y, Z, W;
    X = Y = Z = W = 1;
    std::cin >> X >> Y >> Z >> W;
    const ll mod = 998244353;

    ll a = (Z != 0) ? combination( X, Z, mod ) : X;
    ll b = (W != 0) ? combination( Y, W, mod ) : Y;
    ll c = factorial( X + Y - Z - W - 1, mod );

    ll ans = a * b % mod * c % mod;
    std::cout << ans;
    
    return 0;
}