#include <iostream>
#include <vector>
#include <map>
#include <atcoder/all>
using namespace std;
using namespace atcoder;
typedef long long ll;

ll my_pow(ll x, ll n, ll mod){
    ll ret;
    if (n == 0){
        ret = 1;
    }
    else if (n % 2 == 1){
        ret = (x * my_pow((x * x) % mod, n / 2, mod)) % mod;
    }
    else{
        ret = my_pow((x * x) % mod, n / 2, mod);
    }
    return ret;
}

ll inv(ll x, ll mod){
    return my_pow(x, mod - 2, mod);
}

ll op(ll a, ll b){
    return max(a, b);
}

ll e(){
    return -1e9;
}

ll mod2 = 998244353;

int main(){
    ll H,W,N,P;
    cin >> H >> W >> N >> P;
    vector<ll> x(N);
    vector<ll> y(N);
    for (ll i = 0; i < N; i++){
        cin >> x[i] >> y[i];
    }
    vector<pair<ll,ll>> p(N);
    for (ll i = 0; i < N; i++){
        p[i].first = x[i];
        p[i].second = y[i];
    }
    sort(p.begin(), p.end());
    map<ll, ll> mp;
    mp[1]++;
    for (ll i = 0; i < N; i++){
        mp[y[i]]++;
    }
    ll now = 1;
    for (auto itr = mp.begin(); itr != mp.end(); itr++){
        itr->second = now;
        now++;
    }
    segtree<ll, op, e> seg(now);
    seg.set(mp[1], 0);

    for (ll i = 0; i < N; i++){
        ll prd = seg.prod(0, mp[p[i].second]);
        ll val = seg.get(mp[p[i].second]);
        seg.set(mp[p[i].second], max(val, prd) + 1);
    }
    ll max_omen = seg.prod(0, now);
    //cout << max_omen << endl;
    
    ll ans = (my_pow(P, H + W - 3, mod2));
    ans = (ans - ((my_pow(P - 1, H + W - 3 - max_omen, mod2)) * (my_pow(P - 2, max_omen, mod2))) % mod2 + mod2) % mod2;
    ans = (ans * inv((my_pow(P, H + W - 3, mod2)), mod2)) % mod2;
    cout << ans << endl;
}