#include <stdio.h>
#include <vector>
#include <algorithm>
#define MOD 998244353

struct segTree{
	int value[800010];
	void setValue(int ind, int val, int l=1, int r=200000, int v=1)
	{
		if(l==r) value[v] = val;
		else
		{
			int h = (l+r)/2;
			if(ind<=h) setValue(ind,val,l,h,2*v);
			else setValue(ind,val,h+1,r,2*v+1);
			value[v] = value[2*v]>value[2*v+1]?value[2*v]:value[2*v+1];
		}
	}
	int getMax(int L, int R,int l=1, int r=200000, int v=1)
	{
		if(L<=l&&r<=R) return value[v];
		else if(r<L) return 0;
		else if(R<l) return 0;
		else
		{
			int h = (l+r)/2;
			int s1 = getMax(L,R,l,h,2*v);
			int s2 = getMax(L,R,h+1,r,2*v+1);
			return s1>s2?s1:s2;
		}
	}
}T;

long long int power(long long int a, long long int b)
{
	long long int ans = 1;
	long long int k = a;
	while(b)
	{
		if(b%2==1) ans*=k, ans%=MOD;
		b/=2;
		k*=k, k%=MOD;
	}
	return ans;
}

long long int inv(long long int k)
{
	return power(k,MOD-2);
}

std::pair<int,int> x[200010];
int main()
{
	int a,b,c,d;
	scanf("%d%d%d%d",&a,&b,&c,&d);
	for(int i=1;i<=c;i++)
	{
		int e,f;
		scanf("%d%d",&e,&f);
		x[i] = std::make_pair(e,f);
	}
	std::sort(x+1,x+c+1);
	
	int ans = 0;
	for(int i=1;i<=c;i++)
	{
		int t = T.getMax(1,x[i].second) + 1;
		ans = ans>t?ans:t;
		T.setValue(x[i].second,t);
	}
	
	long long int P = 1;
	for(int i=1;i<=a+b-3;i++) P *= inv(d), P %= MOD;
	for(int i=1;i<=ans;i++) P *= (d-2), P %= MOD;
	for(int i=1;i<=a+b-3-ans;i++) P *= (d-1), P %= MOD;
	printf("%lld",(MOD-P+1)%MOD);
}