#include <bits/stdc++.h>
#include <atcoder/all>
using namespace atcoder;
using namespace std;
using ll=long long;
using ld=double;
ld pie=3.14159265359;
ll mod=998244353;
ll inf=100000;
ll op(ll a,ll b){
    return max(a,b);
}
ll e(){
    return -1;
}
int main(){
    ll h,w,n,p;
    cin >> h >> w >> n >> p;
    vector<ll>x(n),y(n);
    vector<pair<ll,ll>>pp(n);
    for (ll i = 0; i < n; i++)
    {
        cin >> x[i] >> y[i];
        pp[i]={x[i],y[i]};
    }
    sort(pp.begin(),pp.end());
    vector<ll>a(w+1,0);
    segtree<ll,op,e>seg(a);
    for (ll i = 0; i < n; i++)
    {
        ll x=seg.prod(0,pp[i].second+1);
        seg.set(pp[i].second,x+1);
    }
    ll dai=seg.all_prod();
    ll hiku=1;
    ll bo=1;
    for (ll i = 0; i <h-1+w-2-dai; i++)
    {
        hiku*=p-1;
        hiku%=mod;
        bo*=p;
        bo%=mod;
    }
    for (ll i = 0; i < dai; i++)
    {
        hiku*=p-2;
        hiku%=mod;
        bo*=p;
        bo%=mod;
    }
    hiku=mod+bo-hiku;
    hiku%=mod;
    hiku*=inv_mod(bo,mod);
    hiku%=mod;
    cout << hiku << endl;
}