#define _GLIBCXX_DEBUG
#include <bits/stdc++.h>
using namespace std;
using ll = long long; // int64_t
using ull = unsigned long long;
using pll = pair<ll,ll>;
using pii = pair<int,int>;

#define REP(i,m,n) for(int i = m; i <= (n); ++i)
#define rep(i,n) for(int i = 0; i < (n); ++i)
#define rrep(i,n) for(int i = 1; i <= (n); ++i)
#define drep(i,n) for(int i = (n)-1; i >= 0; --i)

const int INF = 1e9+7;   //10oku7

int main() {

  int V, T,S,D;
  cin >> V >> T >> S >> D;
  if (V* T <= D  &&  D <= V*S){
    cout<< "No" << endl;
  } else {
    cout << "Yes" << endl;
  }


}

#include <algorithm>
#include <cfloat>
#include <climits>
#include <cmath>
#include <complex>
#include <cstdio>
#include <cstdlib>
#include <cstring>
#include <functional>
#include <iostream>
#include <map>
#include <memory>
#include <queue>
#include <deque>
#include <set>
#include <sstream>
#include <stack>
#include <string>
#include <utility>
#include <vector>
#include <cassert>
#include <iostream>
#include <stdio.h>
#include <time.h>
 
using namespace std;

typedef long long ll;
 
#define sz size()
#define pb push_back
#define mp make_pair
#define fi first
#define se second
#define all(c) (c).begin(), (c).end()
#define rep(i,a,b) for(ll i=(a);i<(b);++i)
#define per(i,a,b) for(ll i=b-1LL;i>=(a);--i)
#define clr(a, b) memset((a), (b) ,sizeof(a))
#define ctos(c) string(1,c)

#define MOD 1000000007

ll d[20][20];

int main(){
  ll h,w,a,b;
  cin>>h>>w>>a>>b;
  vector<ll> v;
  rep(i,0,b){
    v.pb(0);
  }
  rep(i,0,a){
    v.pb(1);
  }
  ll ans = 0;
  do{
    rep(i,0,1<<a){
      vector<ll> v1;
      rep(j,0,a){
        if((i>>j)&1){
          v1.pb(0);
        }
        else{
          v1.pb(1);
        }
      }
      clr(d,-1);
      rep(y,0,h){
        rep(x,0,w){
          d[y][x] = 0;
        }
      }
      ll flag = 1;
      ll index1 = 0;
      ll index2 = 0;
      rep(y,0,h){
        rep(x,0,w){
          if(d[y][x]!=0)continue;
          if(v[index1]==0){
            d[y][x] = 1;
          }
          else{
            if(v1[index2]==0){
              if(d[y][x+1]==0){
                d[y][x] = 2;
                d[y][x+1] = 2;
              }
              else{
                flag = 0;
              }
            }
            else{
              if(d[y+1][x]==0){
                d[y][x] = 2;
                d[y+1][x] = 2;
              }
              else{
                flag = 0;
              }
            }
            index2++;
          }
          index1++;
        }
      }

      if(flag==1)ans++;
    }
  }while(next_permutation(all(v)));
  cout << ans << endl;
  return 0;
}