// #define _GLIBCXX_DEBUG
#include <bits/stdc++.h>
using namespace std;
#define int long long
#define all(x) (x).begin(), (x).end()
#define rall(x) (x).rbegin(), (x).rend()
#define rep(i, n) for (int i = 0; i < n; ++i)
#define REP(i, n) for (int i = 0; i < n; ++i)
#define range(i,a,b) ((a)<=(i) && (i)<(b))
#define debug(x) cout << #x << ' ' << '=' << ' ' << (x) << endl;
#define fs first
#define sc second
#define pb push_back
#define eb emplace_back
typedef long long ll;
typedef pair<ll, ll> P;
typedef tuple<ll, ll, ll> T;
typedef vector<ll> vec;
typedef vector<P> pvec;
typedef vector<vector<ll>> vvec;
typedef vector<vector<P>> pvvec;
typedef priority_queue<ll> PQI;
typedef priority_queue<P> PQP;
typedef priority_queue<ll,vector<ll>,greater<ll>> PQIG;
typedef priority_queue<P,vector<P>,greater<P>> PQPG;
const vector<int> dx = {0, -1, 0, 1, 1, 1, -1, -1};
const vector<int> dy = {1, 0, -1, 0, 1, -1, 1, -1};
const int MOD = (1000000007);
// const int MOD = (998244353);
// const int INF = (1 << 30);
const int INF = (1LL << 60);
const double EPS = (1 >> 30);
template<class T> inline bool chmin(T& a, T b) {if (a > b) {a = b; return 1;} return 0;}
template<class T> inline bool chmax(T& a, T b) {if (a < b) {a = b; return 1;} return 0;}

template<int MOD> struct modint {
    long long val;

    constexpr modint(long long v = 0) noexcept : val(v % MOD) {
        if (val < 0) v += MOD;
    }
    constexpr modint operator - () const noexcept {
        return val ? MOD - val : 0;
    }
    
    constexpr int getmod() { return MOD; }
    constexpr modint operator + (const modint& r) const noexcept { return modint(*this) += r; }
    constexpr modint operator - (const modint& r) const noexcept { return modint(*this) -= r; }
    constexpr modint operator * (const modint& r) const noexcept { return modint(*this) *= r; }
    constexpr modint operator / (const modint& r) const noexcept { return modint(*this) /= r; }
    constexpr modint& operator += (const modint& r) noexcept {
        val += r.val;
        if (val >= MOD) val -= MOD;
        return *this;
    }
    constexpr modint& operator -= (const modint& r) noexcept {
        val -= r.val;
        if (val < 0) val += MOD;
        return *this;
    }
    constexpr modint& operator *= (const modint& r) noexcept {
        val = val * r.val % MOD;
        return *this;
    }
    constexpr modint& operator /= (const modint& r) noexcept {
        long long a = r.val, b = MOD, u = 1, v = 0;
        while (b) {
            long long t = a / b;
            a -= t * b; swap(a, b);
            u -= t * v; swap(u, v);
        }
        val = val * u % MOD;
        if (val < 0) val += MOD;
        return *this;
    }
    constexpr bool operator == (const modint& r) const noexcept {
        return this->val == r.val;
    }
    constexpr bool operator != (const modint& r) const noexcept {
        return this->val != r.val;
    }
    friend constexpr ostream& operator << (ostream &os, const modint<MOD>& x) noexcept {
        return os << x.val;
    }
    friend constexpr istream& operator >> (istream &is, modint<MOD>& x) noexcept {
        return is >> x.val;
    }
    friend constexpr modint<MOD> modpow(const modint<MOD> &a, long long n) noexcept {
        if (n == 0) return 1;
        auto t = modpow(a, n / 2);
        t = t * t;
        if (n & 1) t = t * a;
        return t;
    }
};
using mint = modint<MOD>;
typedef vector<mint> mvec;
typedef vector<vector<mint>> mvvec;

// 二項係数ライブラリ
template<class T> struct BC {
    vector<T> fact_, inv_, finv_;
    constexpr BC() {}
    constexpr BC(int n) noexcept : fact_(n, 1), inv_(n, 1), finv_(n, 1) {
        init(n);
    }
    constexpr void init(int n) noexcept {
        fact_.assign(n, 1);
        inv_.assign(n, 1);
        finv_.assign(n, 1);
        for(int i = 2; i < n; i++){
            fact_[i] = fact_[i-1] * i;
            inv_[i] = -inv_[MOD%i] * (MOD/i);
            finv_[i] = finv_[i-1] * inv_[i];
        }
    }
    constexpr T C(int n, int k) const noexcept {
        if (n < k || n < 0 || k < 0) return 0;
        return fact_[n] * finv_[k] * finv_[n-k];
    }
    constexpr T P(int n, int k) const noexcept {
        if (n < k || n < 0 || k < 0) return 0;
        return fact_[n] * finv_[n-k];
    }
    constexpr T H(int n, int k) const noexcept {
        return C(n + k - 1, k);
    }
    constexpr T fact(int n) const noexcept {
        if (n < 0) return 0;
        return fact_[n];
    }
    constexpr T inv(int n) const noexcept {
        if (n < 0) return 0;
        return inv_[n];
    }
    constexpr T finv(int n) const noexcept {
        if (n < 0) return 0;
        return finv_[n];
    }
}; // BC<mint> bc(100000);

signed main()
{
    ios::sync_with_stdio(false);
    cin.tie(0);
    cout << fixed << setprecision(15);
    //---------------------------------------------
    
    int h,w,a,b;
    cin>>h>>w>>a>>b;
    BC<mint> bc(200000);
    a=h-a;
    a--; b--;
    h--; w--;
    mint ans=bc.fact(h+w)*bc.finv(h)*bc.finv(w);
    // cout<<ans<<endl;
    for(int i=a+1;i<=h;i++){
        ans-=bc.fact(i+b)*bc.finv(i)*bc.finv(b)*bc.fact(h+w-i-(b+1))*bc.finv(h-i)*bc.finv(w-(b+1));
        // cout<<i+b<<" "<<i<<" "<<b<<endl;
        // cout<<h+w-i-b-2<<" "<<h-i<<" "<<w-b-1<<endl;
        // cout<<i<<endl;
    }
    cout<<ans<<endl;
    
}

Measured memory_bytes: 4992