#include <stdio.h>

long long power_mod (long long a, long long b, long long mod_num) {
  long long ans = 1LL;
  
  if (b > 0LL) {
    ans = power_mod(a, b/2LL, mod_num);
    ans = (ans * ans) % mod_num;
    if (b%2LL == 1LL) {
      ans = (ans * (a % mod_num)) % mod_num;
    }
  }
  
  return ans;
}

int main () {
  int x = 0;
  int y = 0;
  int z = 0;
  int w = 0;
  
  int res = 0;
  
  long long ans = 0LL;
  long long mod_num = 998244353LL;
  
  long long fact[600001] = {};
  long long invf[600001] = {};
  
  res = scanf("%d", &x);
  res = scanf("%d", &y);
  res = scanf("%d", &z);
  res = scanf("%d", &w);
  
  fact[0] = 1LL;
  for (int i = 0; i < x+y; i++) {
    fact[i+1] = fact[i];
    fact[i+1] *= (long long)(i+1);
    fact[i+1] %= mod_num;
  }
  
  invf[x+y] = power_mod(fact[x+y], mod_num-2LL, mod_num);
  for (int i = x+y; i > 0; i--) {
    invf[i-1] = invf[i];
    invf[i-1] *= (long long)i;
    invf[i-1] %= mod_num;
  }
  
  ans = fact[x];
  ans *= invf[z];
  ans %= mod_num;
  ans *= fact[y];
  ans %= mod_num;
  ans *= invf[w];
  ans %= mod_num;
  ans *= fact[x+y-1-z-w];
  ans %= mod_num;
  if (z == 0) {
    ans *= invf[x-1];
    ans %= mod_num;
    ans *= invf[y-w];
    ans %= mod_num;
  } else {
    ans *= invf[y-1];
    ans %= mod_num;
    ans *= invf[x-z];
    ans %= mod_num;
  }
  
  printf("%lld\n", ans);
  return 0;
}