void main(){
	int a, b, c, d;
	readf("%d %d %d %d\n", &a, &b, &c, &d);
	double[2] live;
	live[0] = (a%d==0)? a/d: a/d+1;
	live[1] = (c%b==0)? c/b: c/b+1;
	if(live[0] >= live[1])writeln("Yes");
	else writeln("No");
}

import std.stdio, std.conv, std.algorithm, std.numeric, std.string, std.math;

// 1要素のみの入力
T _scan(T= int)(){
	return to!(T)( readln().chomp() );
}

// 1行に同一型の複数入力
T[] _scanln(T = int)(){
	T[] ln;
	foreach(string elm; readln().chomp().split()){
		ln ~= elm.to!T();
	}
	return ln;
}
