import std.algorithm;
import std.conv;
import std.math;
import std.range;
import std.stdio;
import std.string;
import std.typecons;

bool test (int a, int b, int c, int d) {
  while (true) {
    //health, strength
    c -= b;
    if (c <= 0) return true;
    a -= d;
    if (a <= 0) return false;
  }
}

void main() {
  int a, b, c, d;
  readf (" %d %d %d %d", a, b, c, d);
  writeln (test (a, b, c, d) ? "Yes" : "No");
}

