#include <iostream>
#include <algorithm>
#include <string>
using namespace std;
#define int long long
signed main() {
	int h, w, s, t; cin >> h >> w >> s >> t;
	if (!(h % 2) || !(w % 2))cout << "Yes\n";
	else {
		cout << ((s + t) % 2 ? "No\n" : "Yes\n");
	}
}
