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

struct Fast {Fast() {std::cin.tie(0); ios::sync_with_stdio(false);}} fast;

using ull = unsigned long long;
using ll = long long;
using vi = vector<int>;
using vl = vector<long>;
using vll = vector<long long>;
using vvi = vector<vi>;
using vvl = vector<vl>;
using vvll = vector<vll>;
using vs = vector<string>;
using pii = pair<int, int>;

#define pb push_back
#define mp make_pair
#define YESNO(bool) if(bool){cout<<"YES"<<endl;}else{cout<<"NO"<<endl;}
#define yesno(bool) if(bool){cout<<"yes"<<endl;}else{cout<<"no"<<endl;}
#define YesNo(bool) if(bool){cout<<"Yes"<<endl;}else{cout<<"No"<<endl;}

#define reps(i, a, n) for (ll i = (a); i < (ll)(n); ++i)
#define rep(i, n) reps(i, 0, n)
#define rrep(i, n) reps(i, 1, n + 1)
#define repd(i,n) for(ll i=n-1;i>=0;i--)
#define rrepd(i,n) for(ll i=n;i>=1;i--)

#define debug(x) cerr << "\033[33m(line:" << __LINE__ << ") " << #x << ": " << x << "\033[m" <<endl;
#define kd(x) cerr << "\033[33m" << #x << ": " << x << ", \033[m";
#define kdl(x) cerr << "\033[33m(line:" << __LINE__ << ") " << #x << ": " << x << ", \033[m";
#define kde(x) cerr << "\033[33m" << #x << ": " << x << ", \033[m" << endl;

inline int in_int() {int x; cin >> x; return x;}
inline ll in_ll() {ll x; cin >> x; return x;}
inline string in_str() {string x; cin >> x; return x;}
template <typename T> inline bool chmin(T& a, const T& b) {bool compare = a > b; if (a > b) a = b; return compare;}
template <typename T> inline bool chmax(T& a, const T& b) {bool compare = a < b; if (a < b) a = b; return compare;}

ll dfs(int i, int *v, const int n, int a, int w)
{
    //kd(i); kde(a);
    if (a == 0) return 1;
    if (i+1 == n) return 0;
    if (v[i] == 1) return dfs(i+1, v, n, a, w);
    int *u = new int[n];
    rep(j,n) u[j] = v[j];
    ll ret = 0;
    // try 1
    u[i] = 1;
    if (i+1 < n && (i+1) % w && u[i+1] != 1) {
        u[i+1] = 1;
        ret += dfs(i+1, u, n, a-1, w);
        u[i+1] = 0;
    }
    if (i+w < n && u[i+w] != 1) {
        u[i+w] = 1;
        ret += dfs(i+1, u, n, a-1, w);
        u[i+w] = 0;
    }
    // try 0
    u[i] = 0;
    ret += dfs(i+1, u, n, a, w);
    delete [] u;
    return ret;
}

int main()
{
    int h = in_int();
    int w = in_int();
    int a = in_int();
    int b = in_int();
    int *v = new int[h*w];
    rep(j,h*w) v[j] = 0;
    cout << dfs(0, v, h*w, a, w);
    return 0;
}

#include <iostream>
#include <algorithm>
#include <list>
#include <string>

int h, w;

int f (int a, int b, std::list<int> r) {
  int s = 0;
  if (a == 0 || r.empty()) {
    s = 1;
  } else {
    int m = r.front();

    r.pop_front();

    if (b > 0) {
      s += f(a, b-1, r);
    }

    if ((m+1) % w != 0 && m+1 == r.front()) {
      r.pop_front();
      s += f(a-1, b, r);
      r.push_front(m+1);
    }

    auto i = r.begin();
    while(i != r.end() && *i < m+w) i++;
    if (*i == m+w) {
      auto next = std::next(i);
      r.erase(i);
      s += f(a-1, b, r);
      r.insert(next, m+w);
    }
  }

  return s;
}

int main() {
  int a, b;

  std::cin >> h >> w >> a >> b;

  std::list<int> r;

  for(int i = 0 ; i < h*w; i++) r.push_back(i);

  int s = f(a, b, r);
  std::cout << s << std::endl;

  return 0;
}
