#include<bits/stdc++.h>
 using namespace std;
#define INF 1000000000
#define REP(i,n) for(int (i)=0;(i)<(int)(n);(i)++)
typedef long long LL;
int main(){
    LL H,W,N,K;
    cin>>H>>W>>N>>K;
    if((H+W-2)%N+1==K){
       cout<<"YES"<<endl;
    }else{
       cout<<"NO"<<endl;
    }
}