#include <bits/stdc++.h>
#include <ext/pb_ds/assoc_container.hpp>
using namespace std;
using namespace __gnu_pbds;
template <typename T> using ordered_set = tree<T, null_type, less<T>, rb_tree_tag, tree_order_statistics_node_update>;

#ifndef aa
#define trace(...)
#define endl '\n'
#endif
#define pb push_back
#define ub upper_bound
#define lb lower_bound
#define fi first
#define se second
//#define int long long
typedef long long ll;
typedef long double ld;
#define pii pair<int,int>
#define pll pair<ll,ll>
#define sz(x) ((long long)x.size())
#define fr(a,b,c) for(int a=b; a<=c; a++)
#define frev(a,b,c) for(int a=c; a>=b; a--)
#define rep(a,b,c) for(int a=b; a<c; a++)
#define trav(a,x) for(auto &a:x)
#define all(con) con.begin(),con.end()
#define done(x) {cout << x << endl;return;}
#define mini(x,y) x=min(x,y)
#define maxi(x,y) x=max(x,y)
const ll infl = 0x3f3f3f3f3f3f3f3fLL;
const int infi = 0x3f3f3f3f;
mt19937_64 mt(chrono::steady_clock::now().time_since_epoch().count());
//const int mod = 998244353;
const int mod = 1e9 + 7;
typedef vector<int> vi;
typedef vector<string> vs;
typedef vector<vector<int>> vvi;
typedef vector<pair<int, int>> vpii;
typedef map<int, int> mii;
typedef set<int> si;
typedef set<pair<int,int>> spii;
typedef queue<int> qi;
uniform_int_distribution<int> rng(1,1e5);
uniform_int_distribution<int> rng1(0,1);
uniform_int_distribution<int> rng2(1,5e4);

//DEBUG FUNCTIONS START
#define cerr cout
void __print(int x) {cerr << x;}
void __print(double x) {cerr << x;}
void __print(long double x) {cerr << x;}
void __print(char x) {cerr << '\'' << x << '\'';}
void __print(const char *x) {cerr << '\"' << x << '\"';}
void __print(const string &x) {cerr << '\"' << x << '\"';}
void __print(bool x) {cerr << (x ? "true" : "false");}
template<typename T, typename V>
void __print(const pair<T, V> &x) {cerr << '{'; __print(x.first); cerr << ','; __print(x.second); cerr << '}';}
template<typename T>
void __print(const T &x) {int f = 0; cerr << '{'; for (auto &i: x) cerr << (f++ ? "," : ""), __print(i); cerr << "}";}
void _print() {cerr << "\n";}
template <typename T, typename... V>
void _print(T t, V... v) {__print(t); if (sizeof...(v)) cerr << ", "; _print(v...);}
#ifndef ONLINE_JUDGE
//#define deb(x...) cerr << "[" << #x << "] = "; _print(x)
#define deb(x...)  _print(x)
#else
#define deb(x...)
#endif
// DEBUG FUNCTIONS END



const int N = 2e5 + 5;

int powm(int a, int b){
    int res = 1;
    while (b) {
        if (b & 1)
            res = res * a % mod;
        a = a * a % mod;
        b >>= 1;
    }
    return res;
}


void solve(){
	
	int h, w, a, b, ans = 0;
	cin >> h >> w >> a >> b;
	
	rep(msk, 0, 1<<(h*w)){
		
		if(__builtin_popcount(msk) != a)
			continue;
			
		
		vpii v;
		vvi vis1(h, vi(w));
		
		rep(j,0,h*w){
			if(msk >> j & 1){
				v.pb({j/w, j%w});
				vis1[j/w][j%w] = 1;
			}
		}
		
		rep(msk1, 0, 1<<a){
			vvi vis = vis1;
			bool ok = 1;
			rep(j,0,a){
				int r = v[j].fi, c = v[j].se;
				
				if(msk1 >> j & 1){
					if(r < h-1){
						ok &= !vis[r+1][c];
						vis[r+1][c] = 1;
					}else
						ok = 0;
				}
				else{
					if(c < w-1){
						ok &= !vis[r][c+1];
						vis[r][c+1] = 1;
					}else
						ok = 0;
				}
				if(!ok)
					break;
			}
			ans += ok;
		}
		
		
	}
	
	cout << ans << endl;
	
}





signed main() {
	
    ios_base::sync_with_stdio(0), cin.tie(0), cout.tie(0);
    cout << fixed << setprecision(15);
    int t = 1;
    //cin >> t;
    while (t--)
        solve();
    return 0;
}



int divide(int a, int b) {
    return (a % mod) * powm(b % mod, mod - 2) % mod;
}

#include <bits/stdc++.h>
using namespace std;
int h, w, a, b, ans;
bool vis[18][18];
void dfs(int x, int y, int lef){
	if (y>w) x++, y=1;
	if (x==h&&y==w){
		if (lef==0) ans++;
		return;
	}
	dfs(x, y+1, lef);
	if (lef!=0&&!vis[x][y]){
		if (!vis[x+1][y]){
			vis[x][y]=1, vis[x+1][y]=1;
			dfs(x, y+1, lef-1);
			vis[x][y]=0, vis[x+1][y]=0;
		}
		if (!vis[x][y+1]){
			vis[x][y]=1, vis[x][y+1]=1;
			dfs(x, y+1, lef-1);
			vis[x][y]=0, vis[x][y+1]=0;
		}
	}
	return;
}
int main(){
	for (int i=0; i<=17; i++)
		for (int j=0; j<=17; j++) vis[i][j]=1;
	cin >> h >> w >> a >> b;
	for (int i=1; i<=h; i++)
		for (int j=1; j<=w; j++) vis[i][j]=0;
	dfs (1, 1, a);
	cout << ans << endl;
	return 0;
}
