import std.stdio, std.conv, std.string, std.array, std.range, std.algorithm, std.container;
import std.math, std.random, std.bigint, std.datetime, std.format;
void main(string[] args){ if(args.length > 1) if(args[1] == "-debug") DEBUG = 1; solve(); } bool DEBUG = 0; 
void log(A ...)(lazy A a){ if(DEBUG) print(a); }
void print(){ writeln(""); } void print(T)(T t){ writeln(t); } void print(T, A ...)(T t, A a){ write(t, " "), print(a); }
string unsplit(T)(T xs){ return xs.array.to!(string[]).join(" "); }
string scan(){ static string[] ss; while(!ss.length) ss = readln.chomp.split; string res = ss[0]; ss.popFront; return res; }
T scan(T)(){ return scan.to!T; } T[] scan(T)(int n){ return n.iota.map!(i => scan!T()).array; }
T lowerTo(T)(ref T x, T y){ if(x > y) x = y; return x; } T raiseTo(T)(ref T x, T y){ if(x < y) x = y; return x; }

// ----- ----- ----- ----- ----- ----- ----- ----- ----- ----- ----- ----- //

const long mod = 998244353;
void solve(){
    int a = scan!int, b = scan!int, c = scan!int, d = scan!int;
    auto sf = new long[][](c + 1, d + 1);

    foreach(i; a .. c + 1) foreach(j; b .. d + 1){
        if(i == a && j == b) sf[i][j] = 1;
        else sf[i][j] = (sf[i][j - 1] * i + sf[i - 1][j] * j
          + mod - sf[i - 1][j - 1] * (i - 1) * (j - 1)) % mod;
    }
    sf[c][d].print;
}

