#include <cstdio>
#include <cmath>
#include <iostream>
#include <set>
#include <algorithm>
#include <vector>
#include <map>
#include <cassert>
#include <string>
#include <cstring>
#include <queue>

using namespace std;

#define rep(i,a,b) for(int i = a; i < b; i++)
#define S(x) scanf("%d",&x)
#define S2(x,y) scanf("%d%d",&x,&y)
#define P(x) printf("%d\n",x)
#define all(v) v.begin(),v.end()
#define FF first
#define SS second
#define pb push_back
#define mp make_pair

typedef long long int LL;
typedef pair<int, int > pii;
typedef vector<int > vi;

int h,w,a,b;

int dp[1 << 4][16][16][9];

int bit(int mask, int x) {
  return (mask >> x) & 1;
}

int solve(int mask, int x, int y, int c) {
  if(c < 0) {
    return 0;
  }

  if(x == h) {
    if(mask == 0 && c == 0) {
      return 1;
    }
    return 0;
  }

  int &res = dp[mask][x][y][c];

  int nx = x, ny = y + 1;
  if(ny == w) {
    nx = x + 1;
    ny = 0;
  }

  if(bit(mask, y)) {
    return res = solve(mask & (~(1 << y)), nx, ny, c);
  }

  res = solve(mask, nx, ny, c);
  if(y + 1 < w && bit(mask, y + 1) == 0) {
    res += solve(mask | (1 << (y + 1)), nx, ny, c - 1);
  }
  if(x + 1 < h) {
    res += solve(mask | (1 << y), nx, ny, c - 1);
  }
  return res;
}

int main() {
  scanf("%d%d%d%d",&h,&w,&a,&b);
  if(w > h) swap(w, h);
  memset(dp, -1, sizeof(dp));
  P(solve(0, 0, 0, a));
  return 0;
}

#include <bits/stdc++.h>

#define pb push_back
#define mp make_pair
#define X first
#define Y second
using namespace std;

typedef long long int ll;
typedef vector <int> vi;
typedef pair <int,int> pii;
const int Size=1e6+10;
const int INF=0x3f3f3f3f;

inline int read()
{
    int x=0, f=1; char ch=getchar();
    while(ch<'0' || ch>'9') {if(ch=='-') f=-1; ch=getchar();}
    while(ch>='0' && ch<='9') {x=x*10+ch-'0'; ch=getchar();}
    return x*f;
}

struct node{
    int type,x,y;
};
int h,w,a,b;
node f[20];
int cnt=0;

bool check(int pos,int type,int x,int y)
{
    for (int i=1;i<=pos-1;++i)
    {
        if (f[i].type==0 && type==0 && f[i].y==y && f[i].x==x-1) return false;
        else if (f[i].type==0 && type==1 &&
                 ( (f[i].x==x-1 && f[i].y==y)
                  || (f[i].x==x && f[i].y==y)
                  || (f[i].x==x-1 && f[i].y==y+1)
                  || (f[i].x==x && f[i].y==y+1) ) ) return false;
        else if (f[i].type==1 && type==1 && f[i].x==x && f[i].y==y-1) return false;
    }
    return true;
}

void dfs(int pos,int pre)
{
    if (pos==a+1)
    {
        cnt++;
        return;
    }
    for (int k=pre+1;k<=(h-1)*w+(w-1)*h;++k)
    {
        int i,j;
        if (k<=(h-1)*w)
        {
            if (k%w!=0) {i=k/w+1; j=k%w;}
            else {i=k/w; j=w;}
            if (check(pos,0,i,j))
            {
                f[pos]=(node){0,i,j};
                dfs(pos+1,(i-1)*w+j);
            }
        }
        else
        {
            int kk=k-(h-1)*w;
            if (kk%(w-1)!=0) {i=kk/(w-1)+1; j=kk%(w-1);}
            else {i=kk/(w-1); j=w-1;}
            if (check(pos,1,i,j))
            {
                f[pos]=(node){1,i,j};
                dfs(pos+1,(h-1)*w+(i-1)*(w-1)+j);
            }
        }
    }
}

int main()
{
    h=read(),w=read(),a=read(),b=read();
    dfs(1,0);
    printf("%d\n",cnt);
    return 0;
}
