#include <bits/stdc++.h>

using namespace std;
#define int long long
const int p=998244353;
int po(int a,int b) {if(b==0) return 1; if(b==1) return a; if(b%2==0) {int u=po(a,b/2);return (u*u)%p;} else {int u=po(a,b-1);return (a*u)%p;}}
int inv(int x) {return po(x,p-2);}
int lis(int n,vector<int> a) {
    vector<int> b;for(int i=0;i<n;++i) b.push_back(a[i]);
    sort(b.begin(),b.end());b.erase(unique(b.begin(),b.end()),b.end());
    for(int &x:a) x=lower_bound(b.begin(),b.end(),x)-b.begin();
    int dp[n+2];int cur[n+1];int pr[n];fill(dp,dp+n+2,1e18);dp[0]=(-1);fill(cur,cur+n+1,-1);
    for(int i=0;i<n;++i)
    {
        int x=a[i];
        int pos=lower_bound(dp,dp+n+1,x)-dp-1;
        pr[i]=cur[pos];if(x<dp[pos+1]) {dp[pos+1]=x;cur[pos+1]=i;}
    }
    for(int i=0;i<=n+1;++i)
    {
        if(dp[i]==1e18)
        {
            --i;
            vector<int> v;int cur1=cur[i];
            while(true)
            {
                if(cur1==(-1)) break;
                v.push_back(cur1);
                cur1=pr[cur1];
            }
            reverse(v.begin(),v.end());
            return v.size();
        }
    }
    return 0;
}
int32_t main()
{
    ios_base::sync_with_stdio(false);cin.tie(0);cout.tie(0);
    int h,w,n,t;
    cin>>h>>w>>n>>t;
    int p1=inv(t);int p2=(2*p1)%p;
    vector<pair<int,int> > a;
    for(int i=0;i<n;++i) {int x,y;cin>>x>>y;a.push_back({x,y});}
    sort(a.begin(),a.end());
    vector<pair<int,int> > moms;for(int i=0;i<a.size();++i) moms.push_back({a[i].second,i});
    sort(moms.begin(),moms.end());
    vector<int> v;
    for(int i=0;i<a.size();++i)
    {
        v.push_back(lower_bound(moms.begin(),moms.end(),make_pair(a[i].second,i))-moms.begin());
    }
    int sz=lis(v.size(),v);
    int ap=1;
    for(int i=0;i<sz;++i)
    {
        ap*=(1-p2);ap%=p;
    }
    for(int i=0;i<h+w-3-sz;++i)
    {
        ap*=(1-p1);ap%=p;
    }
    cout<<(((1-ap)%p)+p)%p;
    return 0;
}