#include <bits/stdc++.h>

using namespace std;
using ll = long long;

const ll modc = 1e9+7;
class mint {
    ll x;
public:
    mint(ll x=0) : x((x%modc+modc)%modc) {}
    mint operator-() const {
      return mint(-x);
    }
    mint& operator+=(const mint& a) {
        if ((x += a.x) >= modc) x -= modc;
        return *this;
    }
    mint& operator-=(const mint& a) {
        if ((x += modc-a.x) >= modc) x -= modc;
        return *this;
    }
    mint& operator*=(const  mint& a) {
        (x *= a.x) %= modc;
        return *this;
    }
    mint operator+(const mint& a) const {
        mint res(*this);
        return res+=a;
    }
    mint operator-(const mint& a) const {
        mint res(*this);
        return res-=a;
    }
    mint operator*(const mint& a) const {
        mint res(*this);
        return res*=a;
    }
    mint pow(ll t) const {
        if (!t) return 1;
        mint a = pow(t>>1);
        a *= a;
        if (t&1) a *= *this;
        return a;
    }
    mint inv() const {
        return pow(modc-2);
    }
    mint& operator/=(const mint& a) {
        return (*this) *= a.inv();
    }
    mint operator/(const mint& a) const {
        mint res(*this);
        return res/=a;
    }
    bool operator == (const mint& a) const{
        return x == a.x;
    }
    friend ostream& operator<<(ostream& os, const mint& m){
        os << m.x;
        return os;
    }
    friend istream& operator>>(istream& ip, mint &m) {
        ll t;
        ip >> t;
        m = mint(t);
        return ip;
    }
    ll val(){
        return x;
    }
};

int main(){

    ll H, W, N, K, mi, K2;
    cin >> H >> W >> N >> K;
    K2 = K*K;
    vector<mint> cnt(K2+1), ch(K+1), cw(K+1);

    if (K*2 <= H){
        for (int i=1; i<=K; i++) ch[i] += 2;
        ch[K] += H-K*2;
    }
    else{
        for (int i=1; i<=H-K; i++) ch[i] += 2;
        ch[H-K+1] += H-(H-K)*2;
    }
    if (K*2 <= W){
        for (int i=1; i<=K; i++) cw[i] += 2;
        cw[K] += W-K*2;
    }
    else{
        for (int i=1; i<=W-K; i++) cw[i] += 2;
        cw[W-K+1] += W-(W-K)*2;
    }

    for (int i=1; i<=K; i++){
        for (int j=1; j<=K; j++) cnt[i*j] += ch[i] * cw[j];
    }

    mint ans=0, M = (H-K+1) * (W-K+1), Minv = M.inv();

    for (int i=1; i<=K2; i++) ans += cnt[i] * (mint(1) - ((M-i)*Minv).pow(N));

    cout << ans << endl;

    return 0;
}