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

#define _p(...) (void)printf(__VA_ARGS__)
#define forr(x,arr) for(auto&& x:arr)
#define _overload3(_1,_2,_3,name,...) name
#define _rep2(i,n) _rep3(i,0,n)
#define _rep3(i,a,b) for(int i=int(a);i<int(b);++i)
#define rep(...) _overload3(__VA_ARGS__,_rep3,_rep2,)(__VA_ARGS__)
#define _rrep2(i,n) _rrep3(i,0,n)
#define _rrep3(i,a,b) for(int i=int(b)-1;i>=int(a);i--)
#define rrep(...) _overload3(__VA_ARGS__,_rrep3,_rrep2,)(__VA_ARGS__)
#define ALL(x) (x).begin(), (x).end()
#define BIT(n) (1LL<<(n))
#define SZ(x) ((int)(x).size())
#define fst first
#define snd second
typedef vector<int> vi;typedef vector<vi> vvi;typedef pair<int,int> pii;typedef vector<pii> vpii;
typedef long long ll;

void Main() {
  int H, W, K;
  ll N;
  cin >> H >> W >> N >> K;

  if (K >= (H+W)) {
    puts("YES");
    return;
  }

  int g = (H+W)%2;
  K--;
  bool keven = K % 2 == 0;

  if (N < H+W-1 && N % 2) {
    int r = (H+W-1) / N;
    if (r % 2) keven = !keven;
  }

  bool kwin;
  if (keven) {
    kwin = g == 0;
  }
  else {
    kwin = g != 0;
  }

  puts(kwin ? "YES" : "NO");
}
int main() { cin.tie(0); ios::sync_with_stdio(false); Main(); return 0; }