#include <bits/stdc++.h>
using namespace std;
using ll = long long;
using Graph = vector<vector<int>>;
const int inf = 1 << 29;
const ll infll = 1LL << 60;
const int mod = 1000000007;
const int mod9 = 998244353;

template<class T> bool chmin(T& a, T b){
    if(a > b){
        a = b;
        return true;
    }
    else return false;
}

template<class T> bool chmax(T& a, T b){
    if(a < b){
        a = b;
        return true;
    }
    else return false;
}

int main(){
    int h, w, a, b;
    cin >> h >> w >> a >> b;

    vector<pair<int, int>> s;
    if(w > 0){
        for(int i=1; i<w; i++){
            for(int j=0; j<h; j++){
                s.push_back(make_pair(i + w * j, i + w * j + 1));
            }
        }
    }

    if(h > 0){
        for(int j=0; j<h-1; j++){
            for(int i=1; i<=w; i++){
                s.push_back(make_pair(w * j + i, w * (j+1) + i));
            }
        }
    }

    if(h == 1 && w == 1){
        cout << 1 << endl;
        return 0;
    }

    int n = s.size();

    vector<bool> used(h * w, false);
    int ans = 0;

    for(int i=0; i<(1 << n); i++){
        int m = 0;
        for(int j=0; j<n; j++){
            if(i & (1 << j)) m++;
        }

        if(m == a){
            used.assign(h * w, false);
            for(int j=0; j<n; j++){
                if(i & (1 << j)){
                    if(used[s[j].first-1]) break;
                    else used[s[j].first-1] = true;

                    if(used[s[j].second-1]) break;
                    else used[s[j].second-1] = true;
                }
                if(j == n-1) ans++;
            }
        }
    }

    cout << ans << endl;


}

#include "bits/stdc++.h"

#define REP(i,num) for(ll i=0;i<(num);++i)
#define FOR(i,c,num) for(ll (i)=(c);(i)<(num);++(i))
#define LOOP(i) while(i--)
#define ALL(c) c.begin(),c.end()
#define PRINTALL(c) for(auto pitr=c.begin();pitr!=c.end();++pitr){cout<<*pitr;if(next(pitr,1)!=c.end())cout<<' ';}cout<<endl;
#define PAIRCOMP(c,comp) [](const pair<ll,ll>& lhs,const pair<ll,ll>& rhs){return lhs.c comp rhs.c;}

using namespace std;
using ll = long long;
using ull = unsigned long long;
using vll = vector<ll>;
using vvll = vector<vector<ll>>;

constexpr ll atcoder_mod = 1e9+7;

template<typename T=ll>
T in(){ T x; cin >> x; return (x); }
template<typename T=ll,typename C=vector<T>>
C vecin(int N){ C x(N);REP(i,N){ x[i]=in<T>(); }return x; }
template<typename T=ll,size_t N>
array<T,N> arrin(){array<T,N> x;REP(i,N){ x[i]=in<T>(); }return x;}

void vout(){ cout << endl; }
template<typename Head,typename... Tail>
void vout(Head&& h,Tail&&... t){ cout << ' ' << h;vout(forward<Tail>(t)...); }
void out(){ cout << endl; }
template<typename Head,typename... Tail>
void out(Head&& h,Tail&&... t){ cout << h;vout(forward<Tail>(t)...); }

template<typename T>
bool chmax(T& a,T b){ if(a<b){ a=b;return true; }return false; }
template<typename T>
bool chmin(T& a,T b){ if(a>b){ a=b;return true; }return false; }

ll dfs(ll H,ll W,ll B,ll u,ll v,ll b,vector<ll> M){
	ll sum=0;
	if(b==B){
		return 1ll;
	}

	if(u+1<W){
		if(!M[u+v*W] && !M[u+1+v*W]){
			M[u+v*W]=M[u+1+v*W]=1;
			if(u+1<W){
				sum += dfs(H,W,B,u+1,v,b+1,M);
			}
			else{
				if(v+1<H){
					sum += dfs(H,W,B,0,v+1,b+1,M);
				}
			}
			M[u+v*W]=M[u+1+v*W]=0;
		}
	}
	if(v+1<H){
		if(!M[u+v*W] && !M[u+(v+1)*W]){
			M[u+v*W]=M[u+(v+1)*W]=1;
			if(u+1<W){
				sum += dfs(H,W,B,u+1,v,b+1,M);
			}
			else{
				if(v+1<H){
					sum += dfs(H,W,B,0,v+1,b+1,M);
				}
			}
			M[u+v*W]=M[u+(v+1)*W]=0;
		}
	}

	if(u+1<W){
		sum += dfs(H,W,B,u+1,v,b,M);
	}
	else if(v+1<H){
		sum += dfs(H,W,B,0,v+1,b,M);
	}
	
	return sum;
}

int main(){
	cin.tie(0);
	ios::sync_with_stdio(false);
	cout<<fixed<<setprecision(10);

	auto [H,W,B,A] = arrin<ll,4>();
	vector<ll> M(H*W,0);
	auto sum = dfs(H,W,B,0,0,0,M);

	out(sum);
	return 0;
}
