#include <bits/stdc++.h>
using namespace std;
#define rep(i, n) for (int i = 0; i < (n); i++)
#define per(i, n) for (int i = (n)-1; i >= 0; i--)
#define rep2(i, l, r) for (int i = (l); i < (r); i++)
#define per2(i, l, r) for (int i = (r)-1; i >= (l); i--)
#define each(e, v) for (auto &e : v)
#define MM << " " <<
#define pb push_back
#define eb emplace_back
#define all(x) begin(x), end(x)
#define rall(x) rbegin(x), rend(x)
#define sz(x) (int)x.size()
using ll = long long;
using pii = pair<int, int>;
using pil = pair<int, ll>;
using pli = pair<ll, int>;
using pll = pair<ll, ll>;

template <typename T>
using minheap = priority_queue<T, vector<T>, greater<T>>;

template <typename T>
using maxheap = priority_queue<T>;

template <typename T>
bool chmax(T &x, const T &y) {
    return (x < y) ? (x = y, true) : false;
}

template <typename T>
bool chmin(T &x, const T &y) {
    return (x > y) ? (x = y, true) : false;
}

template <typename T>
int flg(T x, int i) {
    return (x >> i) & 1;
}

template <typename T>
void print(const vector<T> &v, T x = 0) {
    int n = v.size();
    for (int i = 0; i < n; i++) cout << v[i] + x << (i == n - 1 ? '\n' : ' ');
    if (v.empty()) cout << '\n';
}

template <typename T>
void printn(const vector<T> &v, T x = 0) {
    int n = v.size();
    for (int i = 0; i < n; i++) cout << v[i] + x << '\n';
}

template <typename T>
int lb(const vector<T> &v, T x) {
    return lower_bound(begin(v), end(v), x) - begin(v);
}

template <typename T>
int ub(const vector<T> &v, T x) {
    return upper_bound(begin(v), end(v), x) - begin(v);
}

template <typename T>
void rearrange(vector<T> &v) {
    sort(begin(v), end(v));
    v.erase(unique(begin(v), end(v)), end(v));
}

template <typename T>
vector<int> id_sort(const vector<T> &v, bool greater = false) {
    int n = v.size();
    vector<int> ret(n);
    iota(begin(ret), end(ret), 0);
    sort(begin(ret), end(ret), [&](int i, int j) { return greater ? v[i] > v[j] : v[i] < v[j]; });
    return ret;
}

template <typename S, typename T>
pair<S, T> operator+(const pair<S, T> &p, const pair<S, T> &q) {
    return make_pair(p.first + q.first, p.second + q.second);
}

template <typename S, typename T>
pair<S, T> operator-(const pair<S, T> &p, const pair<S, T> &q) {
    return make_pair(p.first - q.first, p.second - q.second);
}

template <typename S, typename T>
istream &operator>>(istream &is, pair<S, T> &p) {
    S a;
    T b;
    is >> a >> b;
    p = make_pair(a, b);
    return is;
}

template <typename S, typename T>
ostream &operator<<(ostream &os, const pair<S, T> &p) {
    return os << p.first << ' ' << p.second;
}

struct io_setup {
    io_setup() {
        ios_base::sync_with_stdio(false);
        cin.tie(NULL);
        cout << fixed << setprecision(15);
    }
} io_setup;

const int inf = (1 << 30) - 1;
const ll INF = (1LL << 60) - 1;
// const int MOD = 1000000007;
const int MOD = 998244353;

template <int mod>
struct Mod_Int {
    int x;

    Mod_Int() : x(0) {}

    Mod_Int(long long y) : x(y >= 0 ? y % mod : (mod - (-y) % mod) % mod) {}

    static int get_mod() { return mod; }

    Mod_Int &operator+=(const Mod_Int &p) {
        if ((x += p.x) >= mod) x -= mod;
        return *this;
    }

    Mod_Int &operator-=(const Mod_Int &p) {
        if ((x += mod - p.x) >= mod) x -= mod;
        return *this;
    }

    Mod_Int &operator*=(const Mod_Int &p) {
        x = (int)(1LL * x * p.x % mod);
        return *this;
    }

    Mod_Int &operator/=(const Mod_Int &p) {
        *this *= p.inverse();
        return *this;
    }

    Mod_Int &operator++() { return *this += Mod_Int(1); }

    Mod_Int operator++(int) {
        Mod_Int tmp = *this;
        ++*this;
        return tmp;
    }

    Mod_Int &operator--() { return *this -= Mod_Int(1); }

    Mod_Int operator--(int) {
        Mod_Int tmp = *this;
        --*this;
        return tmp;
    }

    Mod_Int operator-() const { return Mod_Int(-x); }

    Mod_Int operator+(const Mod_Int &p) const { return Mod_Int(*this) += p; }

    Mod_Int operator-(const Mod_Int &p) const { return Mod_Int(*this) -= p; }

    Mod_Int operator*(const Mod_Int &p) const { return Mod_Int(*this) *= p; }

    Mod_Int operator/(const Mod_Int &p) const { return Mod_Int(*this) /= p; }

    bool operator==(const Mod_Int &p) const { return x == p.x; }

    bool operator!=(const Mod_Int &p) const { return x != p.x; }

    Mod_Int inverse() const {
        assert(*this != Mod_Int(0));
        return pow(mod - 2);
    }

    Mod_Int pow(long long k) const {
        Mod_Int now = *this, ret = 1;
        for (; k > 0; k >>= 1, now *= now) {
            if (k & 1) ret *= now;
        }
        return ret;
    }

    friend ostream &operator<<(ostream &os, const Mod_Int &p) { return os << p.x; }

    friend istream &operator>>(istream &is, Mod_Int &p) {
        long long a;
        is >> a;
        p = Mod_Int<mod>(a);
        return is;
    }
};

using mint = Mod_Int<MOD>;

template <typename Monoid>
struct Segment_Tree {
    using M = typename Monoid::V;
    int n, m;
    vector<M> seg;

    // f(f(a,b),c) = f(a,f(b,c)), f(e1,a) = f(a,e1) = a

    Segment_Tree(const vector<M> &v) : n(v.size()) {
        m = 1;
        while (m < n) m <<= 1;
        seg.assign(2 * m, Monoid::id);
        copy(begin(v), end(v), begin(seg) + m);
        for (int i = m - 1; i > 0; i--) seg[i] = Monoid::merge(seg[2 * i], seg[2 * i + 1]);
    }

    Segment_Tree(int n, const M &x) : Segment_Tree(vector<M>(n, x)) {}

    void update(int i, const M &x, bool apply = false) {
        seg[i + m] = apply ? Monoid::merge(seg[i + m], x) : x;
        i += m;
        while (i >>= 1) seg[i] = Monoid::merge(seg[2 * i], seg[2 * i + 1]);
    }

    M query(int l, int r) const {
        l = max(l, 0), r = min(r, n);
        M L = Monoid::id, R = Monoid::id;
        l += m, r += m;
        while (l < r) {
            if (l & 1) L = Monoid::merge(L, seg[l++]);
            if (r & 1) R = Monoid::merge(seg[--r], R);
            l >>= 1, r >>= 1;
        }
        return Monoid::merge(L, R);
    }

    M operator[](int i) const { return seg[i + m]; }

    template <typename C>
    int find_subtree(int i, const C &check, M &x, int type) const {
        while (i < m) {
            M nxt = type ? Monoid::merge(seg[2 * i + type], x) : Monoid::merge(x, seg[2 * i + type]);
            if (check(nxt)) {
                i = 2 * i + type;
            } else {
                x = nxt;
                i = 2 * i + (type ^ 1);
            }
        }
        return i - m;
    }

    // check(区間 [l,r] での演算結果) を満たす最小の r (存在しなければ n)
    template <typename C>
    int find_first(int l, const C &check) const {
        M L = Monoid::id;
        int a = l + m, b = 2 * m;
        while (a < b) {
            if (a & 1) {
                M nxt = Monoid::merge(L, seg[a]);
                if (check(nxt)) return find_subtree(a, check, L, 0);
                L = nxt;
                a++;
            }
            a >>= 1, b >>= 1;
        }
        return n;
    }

    // check((区間 [l,r) での演算結果)) を満たす最大の l (存在しなければ -1)
    template <typename C>
    int find_last(int r, const C &check) const {
        M R = Monoid::id;
        int a = m, b = r + m;
        while (a < b) {
            if ((b & 1) || a == 1) {
                M nxt = Monoid::merge(seg[--b], R);
                if (check(nxt)) return find_subtree(b, check, R, 1);
                R = nxt;
            }
            a >>= 1, b >>= 1;
        }
        return -1;
    }
};

// sum
template <typename T>
struct Plus_Monoid {
    using V = T;
    static constexpr V merge(V l, V r) { return l + r; };
    static const V id;
};

template <typename T>
const T Plus_Monoid<T>::id = 0;

// min
template <typename T>
struct Min_Monoid {
    using V = T;
    static constexpr V merge(V l, V r) { return min(l, r); };
    static const V id;
};

template <typename T>
const T Min_Monoid<T>::id = numeric_limits<T>::max();

// max
template <typename T>
struct Max_Monoid {
    using V = T;
    static constexpr V merge(V l, V r) { return max(l, r); };
    static const V id;
};

template <typename T>
const T Max_Monoid<T>::id = numeric_limits<T>::min();

// min count (T：最大値の型、S：個数の型)
template <typename T, typename S>
struct Min_Count_Monoid {
    using V = pair<T, S>;
    static constexpr V merge(V l, V r) {
        if (l.first < r.first) return l;
        if (l.first > r.first) return r;
        return V(l.first, l.second + r.second);
    }
    static const V id;
};

template <typename T, typename S>
const pair<T, S> Min_Count_Monoid<T, S>::id = make_pair(numeric_limits<T>::max(), 0);

// max count (T：最大値の型、S：個数の型)
template <typename T, typename S>
struct Max_Count_Monoid {
    using V = pair<T, S>;
    static constexpr V merge(V l, V r) {
        if (l.first > r.first) return l;
        if (l.first < r.first) return r;
        return V(l.first, l.second + r.second);
    }
    static const V id;
};

template <typename T, typename S>
const pair<T, S> Max_Count_Monoid<T, S>::id = make_pair(numeric_limits<T>::min(), 0);

// 一次関数 ax+b の合成 (左から順に作用)
template <typename T>
struct Affine_Monoid {
    using V = pair<T, T>;
    static constexpr V merge(V l, V r) { return V(l.first * r.first, l.second * r.first + r.second); };
    static const V id;
};

template <typename T>
const pair<T, T> Affine_Monoid<T>::id = make_pair(1, 0);

// モノイドの直積
template <typename Monoid_1, typename Monoid_2>
struct Cartesian_Product_Monoid {
    using V1 = typename Monoid_1::V;
    using V2 = typename Monoid_2::V;
    using V = pair<V1, V2>;
    static constexpr V merge(V l, V r) { return V(Monoid_1::merge(l.first, r.first), Monoid_2::merge(l.second, r.second)); }
    static const V id;
};

template <typename Monoid_1, typename Monoid_2>
const pair<typename Monoid_1::V, typename Monoid_2::V> Cartesian_Product_Monoid<Monoid_1, Monoid_2>::id = make_pair(Monoid_1::id, Monoid_2::id);

// range add range min
template <typename T>
struct Min_Plus_Acted_Monoid {
    using Monoid = Min_Monoid<T>;
    using Operator = Plus_Monoid<T>;
    using M = T;
    using O = T;
    static constexpr M merge(M l, O r) { return l + r; };
};

// range add range max
template <typename T>
struct Max_Plus_Acted_Monoid {
    using Monoid = Max_Monoid<T>;
    using Operator = Plus_Monoid<T>;
    using M = T;
    using O = T;
    static constexpr M merge(M l, O r) { return l + r; };
};

// range add range min count (T：最小値の型、S：個数の型)
template <typename T, typename S>
struct Min_Count_Add_Acted_Monoid {
    using Monoid = Min_Count_Monoid<T, S>;
    using Operator = Plus_Monoid<T>;
    using M = pair<T, S>;
    using O = T;
    static constexpr M merge(M l, O r) { return make_pair(l.first + r, l.second); };
};

// range add range max count (T：最大値の型、S：個数の型)
template <typename T, typename S>
struct Max_Count_Add_Acted_Monoid {
    using Monoid = Max_Count_Monoid<T, S>;
    using Operator = Plus_Monoid<T>;
    using M = pair<T, S>;
    using O = T;
    static constexpr M merge(M l, O r) { return make_pair(l.first + r, l.second); };
};

// range affine range sum
template <typename T>
struct Plus_Affine_Acted_Monoid {
    using Monoid = Cartesian_Product_Monoid<Plus_Monoid<T>, Plus_Monoid<T>>;
    using Operator = Affine_Monoid<T>;
    using M = pair<T, T>;
    using O = pair<T, T>;
    static constexpr M merge(M l, O r) { return M(r.first * l.first + r.second * l.second, l.second); };
};

int main() {
    int H, W, N, P;
    cin >> H >> W >> N >> P;

    vector<vector<int>> ys(H);

    rep(i, N) {
        int x, y;
        cin >> x >> y;
        x--, y--;
        ys[x].eb(y);
    }

    Segment_Tree<Max_Monoid<int>> seg(W, 0);

    rep(i, H) {
        sort(all(ys[i]));
        each(y, ys[i]) {
            seg.update(y, seg.query(0, y + 1) + 1, true); //
        }
    }

    int x = seg.query(0, W);

    mint ng = (mint(P - 1) / mint(P)).pow(H + W - 3 - x) * (mint(P - 2) / mint(P)).pow(x);

    cout << -ng + 1 << '\n';
}