#include<bits/stdc++.h>
using namespace std;

#define INF 1234567890
#define ll long long
#define MOD 998244353

ll pw(ll a, ll n)
{
	ll ret = 1;
	while(n)
	{
		if (n&1) ret=ret*a%MOD;
		a=a*a%MOD;
		n >>= 1;
	}
	return ret;
}

ll inv(ll a)
{
	return pw(a, MOD-2);
}

int N, M, K, P;
int fen[200001];

int Max(int idx)
{
	int ret = 0;
	while(idx)
	{
		ret = max(ret, fen[idx]);
		idx &= idx-1;
	}
	return ret;
}

void Add(int idx, int val)
{
	while(idx <= 200000)
	{
		fen[idx] = max(fen[idx], val);
		idx += idx & -idx;
	}
}

int main()
{
	ios::sync_with_stdio(0); cin.tie(0);
	cin.exceptions(ios::badbit | ios::failbit);
	cin >> N >> M >> K >> P;
	vector<pair<int, int> > v;
	for(int i=0; i<K; i++)
	{
		int y, x;
		cin >> y >> x;
		v.push_back({y, x});
	}
	v.push_back({N, M});
	sort(v.begin(), v.end());

	for(auto [y,x] : v)
	{
		int dp = Max(x) + 1;
		Add(x, dp);

		if (y == N && x == M)
		{
			int cnt = dp - 1;
			int dnt = N+M-1 - cnt - 2;

			ll cval = 2 * inv(P) % MOD;
			ll dval = inv(P);

			ll res = 1;
			while(cnt--) res *= (1-cval), res %= MOD;
			while(dnt--) res *= (1-dval), res %= MOD;
			res = 1-res;

			res %= MOD; res += MOD; res %= MOD;
			cout << res << "\n";
			break;
		}
	}
	return 0;
}