#include<bits/stdc++.h>
#include<atcoder/all>
#define all(a) begin(a),end(a)
#define eb emplace_back
#define ep emplace
#define ef(...) else if(__VA_ARGS__)
#define wh(...) while(__VA_ARGS__)
#define fin(...) rr pp(__VA_ARGS__)
#define RD(T,...) T __VA_ARGS__;li(__VA_ARGS__)
#define LL(...) RD(ll,__VA_ARGS__)
#define ST(...) RD(str,__VA_ARGS__)
#define UL(n,...) u1 __VA_ARGS__;resize({n},__VA_ARGS__);li(__VA_ARGS__)
#define UV(n,...) u1 __VA_ARGS__;resize({n},__VA_ARGS__);vi(__VA_ARGS__)
#define SS(n,...) strs __VA_ARGS__;resize({n},__VA_ARGS__);li(__VA_ARGS__)
#define U2(n,m,...) u2 __VA_ARGS__;resize({n,m},__VA_ARGS__);li(__VA_ARGS__)
#define fe(v,e,...) for(au&&__VA_OPT__([)e __VA_OPT__(,__VA_ARGS__)__VA_OPT__(]):v)
#define fo(i,...) for(au[i,i##stop,i##step]=rng_fo(__VA_ARGS__);i<i##stop;i+=i##step)
#define of(i,...) for(au[i,i##stop,i##step]=rng_of(__VA_ARGS__);i>=i##stop;i-=i##step)
#define debug(...) pp(#__VA_ARGS__,__VA_ARGS__)
#define I(...) template<__VA_ARGS__>
#define J typename
#define O operator
#define au auto
#define cs const
#define ifc if constexpr
#define rr return
#define uu using
namespace my{uu vo=void;vo main();vo solve();}int main(){my::main();}namespace my{uu namespace std;uu namespace atcoder;
uu is=istream;uu os=ostream;uu bo=bool;uu dd=long double;uu ll=long long;uu i128=__int128_t;uu ul=unsigned long long;uu u128=__uint128_t;
I(J T)uu v1=vector<T>;I(J T)uu v2=v1<v1<T>>;uu u1=v1<ll>;uu u2=v2<ll>;uu str=string;uu strs=v1<str>;str sp=" ",nc="",nl="\n";
uu ml=modint998244353;is&O>>(is&i,ml&x){ll t;i>>t;x=t;rr i;}os&O<<(os&o,cs ml&x){rr o<<x.val();}uu m1=v1<ml>;uu m2=v2<ml>;
I(J A,J B=A)struct cp{A a={};B b={};cp(){}cp(A a,B b):a(a),b(b){}cp(pair<A,B>p):a(p.first),b(p.second){}
  cp&O+=(cs cp&c){a+=c.a,b+=c.b;rr*this;}cp O+(cs cp&c)cs{rr cp{*this}+=c;}bo O==(cs cp&c)cs{rr a==c.a&&b==c.b;}
  cp&O-=(cs cp&c){a-=c.a,b-=c.b;rr*this;}cp O-(cs cp&c)cs{rr cp{*this}-=c;}bo O!=(cs cp&c)cs{rr a!=c.a||b!=c.b;}cp O-()cs{rr cp(-a,-b);}
  bo O<(cs cp&c)cs{rr a!=c.a?a<c.a:b<c.b;}bo O>(cs cp&c)cs{rr a!=c.a?a>c.a:b>c.b;}friend os&O<<(os&o,cs cp&c){rr o<<c.a<<sp<<c.b;}
};uu cl=cp<ll>;uu cls=v1<cl>;I(J T)uu qmax=priority_queue<T>;I(J T)uu qmin=priority_queue<T,v1<T>,greater<>>;
I(J T)struct set:std::set<T>{set(v1<T>a={}){fe(a,e)this->ep(e);}};I(J T)struct uset:unordered_set<T>{uset(v1<T>a={}){fe(a,e)this->ep(e);}};
I(J T)struct mset:multiset<T>{mset(v1<T>a={}){fe(a,e)this->ep(e);}vo erase(cs T&x){if(this->contains(x))multiset<T>::erase(this->find(x));}};
I(J T,J U=T)uu map=std::map<T,U>;I(J T,J U=T)uu umap=unordered_map<T,U>;ll ppc(ul x){rr __builtin_popcountll(x);}
ll oo=3e18;dd ee=1e-12;u1 dx{-1,0,1,0,-1,1,1,-1},dy{0,-1,0,1,-1,-1,1,1};str Yes(bo y=1){rr y?"Yes":"No";}str No(){rr"No";}
ll rnd(ll l,ll r=oo){static ul x=76,y=53,z=20,w=41;ul t=x^(x<<11);x=y,y=z,z=w,w=(w^(w>>19))^(t^(t>>8));if(r==oo)r=l,l=0;rr w%(r-l)+l;}
ll l2(u128 x){x|=1;ll r=0;wh(x)x>>=1,++r;rr r;}bo odd(ll x){rr x&1;}ll pwm1(ll x){rr 1-2*(x&1);}I(J T)bo at(T x,ll i){rr x>>i&1;}
ll l10(u128 x){x|=1;ll r=0;wh(x)x/=10,++r;rr r;}bo eve(ll x){rr~x&1;}ll pw2(ll n){rr 1LL<<n;}I(J T,J U,J V)bo in(T l,U m,V r){rr l<=m&&m<r;}
I(J T)T flo(T x,T y){rr y<0?x=-x,y=-y:x>=0?x/y:(x+1)/y-1;}array<ll,3>rng_fo(ll a,ll b=oo,ll c=1){if(b==oo)b=a,a=0;rr{a,b,c};}
I(J T)T cei(T x,T y){rr y<0?x=-x,y=-y:x<=0?x/y:(x-1)/y+1;}array<ll,3>rng_of(ll a,ll b=0,ll c=1){rr{a-1,b,c};}I(J T)T abs(T x){rr x<0?-x:x;}

I(J T)au&O++(v1<T>&v){fe(v,e)++e;rr v;}I(J T)au&O^=(v1<T>&v,cs v1<T>&u){copy(all(u),back_inserter(v));rr v;}
I(J T)au&O--(v1<T>&v){fe(v,e)--e;rr v;}I(J T)au O^(v1<T>v,cs v1<T>&u){rr v^=u;}u1 io(ll n,ll x=0){u1 a;fo(i,n)a.eb(i+x);rr a;}
I(J T,J F=less<>)T&srt(T&a,F f={}){sort(all(a),cref(f));rr a;}I(J T)T&rv(T&a){reverse(all(a));rr a;}
I(J T)T&rsr(T&a){srt(a),rv(a);rr a;}I(J T)T&uq(T&a){srt(a),a.erase(unique(all(a)),end(a));rr a;}I(J T)ll len(cs T&a){rr a.size();}
I(J T)decltype(au)bg(T&a){assert(len(a));rr*begin(a);}I(J T)T pof(deque<T>&q){T r=bg(q);q.pop_front();rr r;}I(J T)constexpr bo isv=0;
I(J T)decltype(au)rb(T&a){assert(len(a));rr*rbegin(a);}I(J T)T pob(deque<T>&q){T r=rb(q);q.pop_back();rr r;}I(J T)constexpr bo isv<v1<T>> =1;
I(J T)au pop(T&a){ifc(isv<T>||is_same_v<T,str>){au r=rb(a);a.pop_back();rr r;}else{au r=a.top();a.pop();rr r;}}
I(J...A)au max(cs A&...a){rr max(initializer_list<common_type_t<A...>>{a...});}I(J T,J U=T)vo af(v1<T>&a,U e={}){a.ep(begin(a),e);}
I(J...A)au min(cs A&...a){rr min(initializer_list<common_type_t<A...>>{a...});}I(J T)vo df(T&a){a.erase(begin(a));}
I(J T,J U)ll arglb(cs v1<T>&a,cs U&b){rr lower_bound(all(a),b)-begin(a);}I(J T,J U)bo amax(T&a,cs U&b){rr a<b?a=b,1:0;}
I(J T,J U)ll argub(cs v1<T>&a,cs U&b){rr upper_bound(all(a),b)-begin(a);}I(J T,J U)bo amin(T&a,cs U&b){rr a>b?a=b,1:0;}
I(J T=ll,ll n,ll i=0)au vec(cs ll(&l)[n],T x={}){ifc(n==i+1)rr vector(l[i],x);else rr vector(l[i],vec<T,n,i+1>(l,x));}
I(J S,bo f(S&,cs S&),J V)au scan(cs V&v){cp<S,bo>r;ifc(!isv<V>)r={v,1};else fe(v,x)if(au t=scan<S,f>(x);t.b)!r.b?r=t,0:f(r.a,t.a);rr r;}
I(J V)au recv(cs V&){ifc(isv<V>)rr recv(J V::value_type());else rr V();}I(J T)bo add(T&a,cs T&b){rr a+=b,1;}
I(J V)au max(cs v1<V>&v){rr scan<decltype(recv(V())),amax>(v).a;}I(J V)au sum(cs v1<V>&v){rr scan<decltype(recv(V())),add>(v).a;}
I(J V)au min(cs v1<V>&v){rr scan<decltype(recv(V())),amin>(v).a;}I(ll n,J...A)vo resize(cs ll(&l)[n],A&...a){((a=vec(l,recv(a))),...);}
I(J V)vo fill(v1<V>&v,decltype(recv(V()))x={}){fe(v,e)ifc(isv<V>)fill(e,x);else e=x;}

struct fio{fio(){ios::sync_with_stdio(0);cin.tie(0);cout<<fixed<<setprecision(l10(1/ee)+1);}}fio;
os&O<<(os&o,cs u128&x){if(x>=10)o<<x/10;rr o<<ll(x%10);}os&O<<(os&o,cs i128&x){rr o<<str(x<0,'-')<<u128(abs(x));}
I(J V)os&O<<(os&o,cs v1<V>&v){str s=nl;ifc(isv<V>){ifc(isv<J V::value_type>)s+=nl;}else s=sp;fe(v,e)o<<e<<(&e==&rb(v)?nc:s);rr o;}
I(J T)os&O<<(os&o,cs set<T>&v){fe(v,e)o<<e<<sp;rr o;}I(J T,J U)os&O<<(os&o,cs map<T,U>&m){fe(m,e)o<<cp(e)<<nl;rr o;}
I(J T)os&O<<(os&o,cs mset<T>&v){fe(v,e)o<<e<<sp;rr o;}I(J T)is&O>>(is&i,v1<T>&v){fe(v,e)i>>e;rr i;}
I(J...A)vo li(A&...a){(cin>>...>>a);}I(J...A)vo vi(A&...a){fo(i,(len(a)&...))(cin>>...>>a[i]);}
I(J...A)vo pp(cs A&...a){ll i=0;((cout<<a<<(++i==sizeof...(a)?nc:sp)),...);cout<<nl;}

struct edg{ll t,w;edg(){}edg(ll t,ll w=1):t(t),w(w){}};uu graph=v2<edg>;
graph tog(cs u2&a){graph g;fe(a,e){g.eb();fe(e,v)rb(g).eb(v);}rr g;}u2 tou(cs graph&g){u2 a;fe(g,e){a.eb();fe(e,v,w)rb(a).eb(v);}rr a;}
I(J G)au ygi(G&g,ll m,bo f=1){ifc(is_same_v<G,u2>){UV(m,a,b);if(f)--a,--b;fo(i,m)g[a[i]].eb(b[i]);rr tuple{a,b};}
  else{UV(m,a,b,c);if(f)--a,--b;fo(i,m)g[a[i]].eb(b[i],c[i]);rr tuple{a,b,c};}}
I(J G)au mgi(G&g,ll m,bo f=1){ifc(is_same_v<G,u2>){au[a,b]=ygi(g,m,f);fo(i,m)g[b[i]].eb(a[i]);rr tuple{a,b};}
  else{au[a,b,c]=ygi(g,m,f);fo(i,m)g[b[i]].eb(a[i],c[i]);rr tuple{a,b,c};}}I(J G)au ti(G&g,bo f=1){rr mgi(g,len(g)-1,f);}
u1 en(cs str&s,cs str&b="a"){u1 r;fe(s,e)r.eb(len(b)==1?e-b[0]:b.find_first_of(e));rr r;}str ins(){ST(s);rr s;}
str de(cs u1&a,cs str&b="a"){str r;fe(a,e)r+=(len(b)==1?e+b[0]:in(0,e,len(b))?b[e]:'|');rr r;}strs inss(ll n){SS(n,s);rr s;}
u2 en(cs strs&s,cs str&b="a"){u2 r;fe(s,e)r.eb(en(e,b));rr r;}strs de(cs u2&a,cs str&b="a"){strs r;fe(a,e)r.eb(de(e,b));rr r;}

I(J...A)u1 zp(A&...a){u1 v=(a^...);uq(v);([&](u1&u){fe(u,e)e=arglb(v,e);}(a),...);rr v;}I(J...A)vo dec(A&...a){((--a),...);}
I(J F,J...A)u1 vs(F f,A&...a){u1 o=io((len(a)&...));srt(o,cref(f));([&](au&e){au c=e;fo(i,len(e))e[i]=c[o[i]];}(a),...);rr o;}
I(J F)ll bsl(F f,ll o,ll n){wh(abs(o-n)>1)(f((o+n)/2)?o:n)=(o+n)/2;rr o;}ll sqr(ll x){ll r=max(sqrtl(x)-1,0.);wh(r+1<=x/(r+1))++r;rr r;}
I(J F)dd bsd(F f,dd o,dd n){fo(t,l2(abs(o-n)/ee)+5)(f((o+n)/2)?o:n)=(o+n)/2;rr o;}I(J T)au zt(v1<T>a){fo(i,1,len(a))a[i]+=a[i-1];rr a;}
cls rle(cs u1&a){cls r;fe(a,e)len(r)&&e==rb(r).a?++rb(r).b:r.eb(e,1).b;rr r;}cls rce(u1 a){rr rle(srt(a));}
i128 pow(i128 x,u128 n,u128 m=0){i128 r=1;wh(n){if(n&1)r*=x;x*=x;if(m)r%=m,x%=m;n>>=1;}rr r;}I(J T)T sq(T a){rr a*a;}
u1 divs(ll n){u1 r;for(ll i=1;i*i<=n;++i)if(n%i==0)r.eb(i),r.eb(n/i);rr uq(r);}I(J T)T cb(T a){rr a*a*a;}
cls fact(ll n){umap<ll>m;for(ll i=2;i*i<=n;++i)wh(n%i==0)++m[i],n/=i;if(n>1)++m[n];cls r;fe(m,e)r.eb(e);rr srt(r);}

uu S=ll;
uu F=ll;
S e(){rr-oo;}
F id(){rr{};}
S op(S a,S b){rr max(a,b);}
S mapping(F f,S x){rr f+x;}
F composition(F f,F g){rr f+g;}

vo main(){ll T=1;fo(t,T)solve();}
vo solve(){
  LL(H,W,N,P);
  UV(N,x,y);dec(x,y);
  
  u2 g(H);
  fo(i,N)g[x[i]].eb(y[i]);
  fe(g,e)srt(e);
  
  lazy_segtree<S,op,e,F,mapping,composition,id>s(v1<S>(W,0));
  
  fo(i,H){
    fe(g[i],j){
      ll k=bsl([&](ll k)->bo{
        if(k==W)rr 1;
        rr s.get(j)+1<=s.get(k);
      },W,j);
      s.apply(j,k,1);
    }
  }
  
  ll K=s.get(W-1);
  ml ans=(1-ml(P).inv()).pow(H+W-3-K)*(1-2*ml(P).inv()).pow(K);
  pp(1-ans);
}}