#include <bits/stdc++.h>

using namespace std;

int main(){
  int h,w,s,t; cin >> h >> w >> s >> t;
  if(h%2==0||w%2==0 || (s==1&&t==1)||(s==h&&t==1)||(s==1&&t==w)||(s==h&&t==w) || (h%2==1&&w%2==1&&(s%2==t%2))) cout << "Yes";
  else cout << "No";
  cout <<endl;

  return 0;
}

