import java.io.*; import java.util.*; import java.util.stream.*; public class Main { static final int MOD = 998244353; public static void main(String[] args) throws Exception { Scanner sc = new Scanner(); int h = sc.nextInt(); int w = sc.nextInt(); int n = sc.nextInt(); int p = sc.nextInt(); TreeMap> places = new TreeMap<>(); for (int i = 0; i < n; i++) { int x = sc.nextInt(); int y = sc.nextInt(); if (!places.containsKey(x)) { places.put(x, new TreeSet<>()); } places.get(x).add(y); } TreeMap current = new TreeMap<>(); current.put(0, 0); for (TreeSet x : places.values()) { TreeMap next = new TreeMap<>(); next.put(0, 0); for (int y : x) { next.put(y, current.floorEntry(y).getValue() + 1); } current = next; } int count = current.lastEntry().getValue(); int all = h + w - 3; long except = pow(p - 2, count) * pow(p - 1, all - count) % MOD * pow(pow(p, all), MOD - 2) % MOD; System.out.println((1 + MOD - except) % MOD); } static long pow(long x, int p) { if (p == 0) { return 1; } else if (p % 2 == 0) { return pow(x * x % MOD, p / 2); } else { return pow(x, p - 1) * x % MOD; } } } class Utilities { static String arrayToLineString(Object[] arr) { return Arrays.stream(arr).map(x -> x.toString()).collect(Collectors.joining("\n")); } static String arrayToLineString(int[] arr) { return String.join("\n", Arrays.stream(arr).mapToObj(String::valueOf).toArray(String[]::new)); } } class Scanner { BufferedReader br = new BufferedReader(new InputStreamReader(System.in)); StringTokenizer st = new StringTokenizer(""); StringBuilder sb = new StringBuilder(); public Scanner() throws Exception { } public int nextInt() throws Exception { return Integer.parseInt(next()); } public long nextLong() throws Exception { return Long.parseLong(next()); } public double nextDouble() throws Exception { return Double.parseDouble(next()); } public int[] nextIntArray() throws Exception { return Stream.of(br.readLine().split(" ")).mapToInt(Integer::parseInt).toArray(); } public String next() throws Exception { while (!st.hasMoreTokens()) { st = new StringTokenizer(br.readLine()); } return st.nextToken(); } }