import std.stdio, std.string, std.conv;
import std.typecons;
import std.algorithm, std.array, std.range, std.container;
import std.math;

void main() {
	auto input = readln.split.to!(int[]);
	auto A = input[0], B = input[1], C = input[2], D = input[3];
	
	writeln( (C%B == 0 ? C/B : C/B+1) <= (A%D == 0 ? A/D : A/D+1) ? "Yes" : "No");
}

