#define NDEBUG
NDEBUG


#include <algorithm>
#include <array>
#include <bitset>
#include <cassert>
#include <cstring>
#include <cmath>
#include <functional>
#include <iomanip>
#include <iostream>
#include <map>
#include <set>
#include <sstream>
#include <string>
#include <tuple>
#include <unordered_map>
#include <unordered_set>
#include <vector>
#include <memory>
#include <queue>
#include <random>


using namespace std;

template<class T>
using vec = std::vector<T>;


// TC_REMOVE_BEGIN
/// caide keep
bool __hack = std::ios::sync_with_stdio(false);
/// caide keep
auto __hack1 = cin.tie(nullptr);
// TC_REMOVE_END


// Section with adoption of array and vector algorithms.


//#include <ext/pb_ds/tree_policy.hpp>
//#include <ext/pb_ds/assoc_container.hpp>
//
//template <class T> using StdTree = tree<T, null_type, less<T>, rb_tree_tag,tree_order_statistics_node_update>;


namespace template_util {
    

    constexpr int bytecount(uint64_t x) {
        return x ? 1 + bytecount(x >> 8) : 0;
    }

    template<int N>
    struct bytetype {
        
    };

    
    /// caide keep
    template<uint64_t N>
    struct minimal_uint : bytetype<bytecount(N)> {
    };
}


template<class T>
T next(istream& in) {
    T ret;
    in >> ret;
    return ret;
}


template<typename T> static constexpr T wrap_pos(T a, T m) { return a < 0 ? a + m : a; }

// m must be positive
template<typename T> static constexpr T mod(T a, T m) { return wrap_pos(a % m, m); }

template<typename T>
static constexpr T inverse2(T a, T m) { return a <= 1 ? a : mod((1 - inverse2(m % a, a) * m) / a, m); }

template<typename T>
static constexpr T inverse(T a, T m) { return inverse2(mod(a, m), m); }

template<typename T, typename C, T Modulus>
class MR
{
 private:
   // indicates value is in range [0, 2 * Modulus)
  struct tag_minus {}; // indicates value is in range (-Modulus, Modulus)
  struct tag_good {}; // indicates value is in range

//  T value;

  static_assert(std::numeric_limits<C>::max() / Modulus / Modulus > 0, "compute type is too small");
  static_assert(Modulus < std::numeric_limits<T>::max() / 2, "storage type is too small");

  
  static constexpr T reduce(T value, tag_minus)
  {
    return value < 0 ? value + Modulus : value;
  }

  static constexpr T reduce(T value, tag_good) { return value; }

 public:
  T value;
  
  
  constexpr MR() : value(0) {}
  constexpr MR(C value) : value(reduce(value % Modulus, tag_minus())) {}
  template<typename tag_t>
  constexpr MR(T value, tag_t tag) : value(reduce(value, tag)) {}

  
  constexpr MR operator *(MR b) const { return MR(C(value) * C(b.value) % Modulus, tag_good()); }
  

  MR &operator -=(MR b) { value = reduce(value - b.value, tag_minus()); return *this; }
  

  constexpr T get() const { return value; }

  // These are only valid if the dividend is relatively prime to the modulus
  constexpr MR inverse() const
  {
    return MR(::inverse(C(value), C(Modulus)), tag_good());
  }
  constexpr MR operator /(MR b) const { return *this * b.inverse(); }
  
};

template<typename T, typename C, T Modulus>
static inline std::ostream &operator<<(std::ostream &o, MR<T, C, Modulus> mr)
{
  return o << mr.get();
}


//template <class T>
//T gcd(T a, T b) {
//    return b == 0 ? a : gcd(b, a % b);
//}

//TODO extended gcd


// MD implementation of factorials and binomial

template<class T>
vector<T> getFactorials(int n) {
  vector<T> res(n);
  res[0] = T(1);
  for (int i = 1; i < n; ++i) {
    res[i] = res[i-1] * i;
  }
  return res;
}


// TODO(alf): Tests


//
//int64_t lcm(const vector<int64_t>& a) {
//    int64_t res = a[0];
//    for (int i = 1; i < (int)a.size(); ++i) {
//        int64_t g = gcd(res, a[i]);
//        res *= a[i];
//        res /= g;
//    }
//    return res;
//}
//
//int64_t lcm(int64_t a, int64_t b) {
//    return (a * b / gcd(a, b));
//}


// TODO: test on timus problem
// vector<double> polynomeEquationSolve() {}


// Algorithms


typedef MR<int, int64_t, 1000000007> md;

const int MAXN = 300000;

vec<md> fs = getFactorials<md>(MAXN);

md C(int n, int k) {
  return fs[n] / fs[k] / fs[n - k];
}

void solve(istream& in, ostream& out) {
  auto n = next<int>(in);
  auto m = next<int>(in);
  auto a = next<int>(in);
  auto b = next<int>(in);

  int N = n + m - 2;
  int K = n - 1;

  md res = C(N, K);
  for (int row = n - a + 1, row2 = a; row <= n; ++row, --row2) {

    N = row + b - 2;
    K = row - 1;

    int N2 = row2 + (m - b) - 2;
    int K2 = row2 - 1;
    res -= C(N, K) * C(N2, K2);

  }

  out << res << "\n";
}

//#include <fstream>


int main() {
//  ifstream fin("bridges.in");
//  ofstream fout("bridges.out");
    solve(cin, cout);
//  solve(fin, fout);
    return 0;
}



Measured memory_bytes: 1408