#include <bits/stdc++.h>
using namespace std;
 
#define REP(i,n) for(int i=0;i<n;i++)
#define rep(i,n) for(int i=0;i<n;i++)
#define INF 1<<29
#define LINF LLONG_MAX/3
#define MP make_pair
#define PB push_back
#define EB emplace_back
#define ALL(v) (v).begin(),(v).end()
#define debug(x) cerr<<#x<<":"<<x<<endl
#define debug2(x,y) cerr<<#x<<","<<#y":"<<x<<","<<y<<endl
template<typename T> ostream& operator<<(ostream& os,const vector<T>& vec){ os << "["; for(const auto& v : vec){ os << v << ","; } os << "]"; return os; }
const long long mod = 1e9+7;
 
typedef long long ll;
typedef unsigned long long ull;
typedef pair<int,int> pii;
typedef vector<int> vi;
typedef vector<vi> vvi;
typedef vector<ll> vll;
typedef vector<vll> vvll;

int main(){
    ll H,W,N,K;cin>>H>>W>>N>>K;
    K--;
    ll t = H+W-1;
    if(t==1){
        if(K==0) cout << "YES" << endl;
        else cout << "NO" << endl;
        return 0;
    }

    ll p=t%N;
    if(p==0){
        if(K==N-1) cout << "YES" << endl;
        else cout << "NO" << endl;
    }else{
        p--;
        if(p==K) cout << "YES" << endl;
        else cout << "NO" << endl;
    }
}