#include<bits/stdc++.h>
#if __has_include(<atcoder/all>)
#include<atcoder/modint>
#include<atcoder/lazysegtree>
#endif
using namespace std;
#define eb emplace_back
#define LL(...) ll __VA_ARGS__;lin(__VA_ARGS__)
#define RDVV(T,n,...) vec<T>__VA_ARGS__;fe(refs(__VA_ARGS__),e)e.get().resizes(n);vin(__VA_ARGS__)
#define VV(n,...) RDVV(ll,n,__VA_ARGS__)
#define fo(i,...) for(auto[i,i##stop,i##step]=for_range<ll>(0,__VA_ARGS__);i<i##stop;i+=i##step)
#define fe(a,e,...) for(auto&&__VA_OPT__([)e __VA_OPT__(,__VA_ARGS__]):a)
#define defpp template<ostream&o=cout>void pp(const auto&...a){[[maybe_unused]]const char*c="";((o<<c<<a,c=" "),...);o<<'\n';}void epp(const auto&...a){pp<cerr>(a...);}
#define entry defpp void main();void main2();}int main(){my::io();my::main();}namespace my{
#define use_ml998244353 using ml=atcoder::modint998244353;
namespace my{
auto&operator<<(ostream&o,const atcoder::modint998244353&x){return o<<(int)x.val();}
void io(){cin.tie(nullptr)->sync_with_stdio(0);cout<<fixed<<setprecision(15);}
using ll=long long;
template<class T>concept modulary=requires(T t){t.mod();};
constexpr auto refs(auto&...a){return array{ref(a)...};}
template<class T>constexpr auto for_range(T s,T b){T a=0;if(s)swap(a,b);return array{a-s,b,1-s*2};}
void lin(auto&...a){(cin>>...>>a);}
void vin(auto&...a){fo(i,(a.size()&...))(cin>>...>>a[i]);}
constexpr ll size10(auto x){x|=1;ll r=0;while(x>0)x/=10,++r;return r;}
template<class T>constexpr ll maxsize10(){return size10(numeric_limits<T>::max());}
template<bool is_negative=false>struct infinity{
  template<integral T>static constexpr T ones(size_t n){return n?ones<T>(n-1)*10+1:0;}
  template<integral T>constexpr operator T()const{static constexpr T v=ones<T>(maxsize10<T>())*(1-is_negative*2);return v;}
  constexpr auto operator-()const{return infinity<!is_negative>();}
};
constexpr infinity oo;
void dec(auto&...a){((--a),...);}
template<class F=less<>>auto&sort(auto&a,F f={}){ranges::sort(a,f);return a;}
template<class...A>using pack_back_t=tuple_element_t<sizeof...(A)-1,tuple<A...>>;
}
namespace my{
template<class V>constexpr int depth=0;
template<class T>struct core_t_helper{using type=T;};
template<class T>using core_t=core_t_helper<T>::type;
template<class V>struct vec;
template<int D,class T>struct hvec_helper{using type=vec<typename hvec_helper<D-1,T>::type>;};
template<class T>struct hvec_helper<0,T>{using type=T;};
template<int D,class T>using hvec=hvec_helper<D,T>::type;
template<class V>struct vec:vector<V>{
  static constexpr int D=depth<V>+1;
  using C=core_t<V>;
  using vector<V>::vector;
  void resizes(const auto&...a){if constexpr(sizeof...(a)==D)*this=make(a...,C{});else{ }}
  static auto make(ll n,const auto&...a){
    if constexpr(sizeof...(a)==1)return vec<C>(n,array{a...}[0]);
    else { }
  }
  vec&operator--(){fe(*this,e)--e;return*this;}
  ll size()const{return vector<V>::size();}
  auto&emplace_back(auto&&...a){vector<V>::emplace_back(std::forward<decltype(a)>(a)...);return*this;}
};
template<class...A>requires(sizeof...(A)>=2)vec(const A&...a)->vec<hvec<sizeof...(A)-2,pack_back_t<A...>>>;
}
namespace my{
namespace sgt{
template<class T,auto x>T identity(){return x;}
template<class T>T max(T a,T b){return a<b?b:a;}
template<class F>F replace_identity(){if constexpr(modulary<F>){ }else return oo;}
template<class S,class F>S replace_mapping(F f,S x){return(f==replace_identity<F>()?x:f);}
template<class F>F replace_composition(F f,F g){return(f!=replace_identity<F>()?f:g);}
template<class T>struct lazyseg_replace_max:atcoder::lazy_segtree<T,max<T>,identity<T,-oo>,T,replace_mapping<T,T>,replace_composition<T>,replace_identity<T>>{
  using atcoder::lazy_segtree<T,max<T>,identity<T,-oo>,T,replace_mapping<T,T>,replace_composition<T>,replace_identity<T>>::lazy_segtree;
  ll ge_leftmost(ll l,const T&x){return this->max_right(l,[&](T v){return v<x;});}
};
}
}
namespace my{entry
void main(){
  LL(H,W,N,P);
  VV(N,x,y);dec(x,y);

  vec<vec<ll>>g(H);
  fo(i,N)g[x[i]].eb(y[i]);

  sgt::lazyseg_replace_max<ll>s(vec<ll>(W,0));
  fo(i,H){
    fe(sort(g[i]),j){
      ll v=s.get(j)+1;
      ll r=s.ge_leftmost(j,v);
      s.apply(j,r,v);
    }
  }

  use_ml998244353
  ll X=s.get(W-1);
  ml p=1-ml(P).inv()*2;
  ml q=1-ml(P).inv();
  pp(1-p.pow(X)*q.pow(H+W-3-X));
}}