#include<bits/stdc++.h>
using namespace std;
using Int = long long;
template<typename T1,typename T2> inline void chmin(T1 &a,T2 b){if(a>b) a=b;}
template<typename T1,typename T2> inline void chmax(T1 &a,T2 b){if(a<b) a=b;}

//INSERT ABOVE HERE
signed main(){
  Int h,w,s,t;
  cin>>h>>w>>s>>t;

  auto YES=[](){cout<<"Yes"<<endl;exit(0);};
  auto NO=[](){cout<<"No"<<endl;exit(0);};
  if(h==1){
    if(s==1||s==w) YES();
    NO();    
  }
  if(w==1){
    if(t==1||t==h) YES();
    NO();
  }
  if(h%2==0||w%2==0) YES();
  if((s+t)%2==0) YES();
  NO();
  return 0;
}

