#include<bits/stdc++.h>

using namespace std;
using ll=long long;
#define rep2(i, a, n) for(int i = (a); i < (n); i++)
#define rep(i, n) rep2(i,0,n)

void flagfunc4(bool flag){cout<<(flag?"YES\n":"NO\n");}
void out(){cout<<endl;} template<typename Head,typename... Tail> void out(Head&& head,Tail&&... tail){cout<<head<<" ";out(forward<Tail>(tail)...);}

int main(){
  cin.tie(nullptr);ios_base::sync_with_stdio(false);
  int h,w;
  cin>>h>>w;
  ll hoge=0,n,k;
  hoge=h*w;
  cin>>n>>k;
  flagfunc4((k==(hoge-1)%n+1));
}