import std.stdio;

void main() {
  int tHp, tAttack, aHp, aAttack;
  
  readf(" %s %s %s %s", &tHp, &tAttack, &aHp, &aAttack);
  
  for (;;) {
    aHp -= tAttack;
    if (aHp <= 0) {
      writeln("Yes");
      return;
    }
    tHp -= aAttack;
    if (tHp <= 0) {
      writeln("No");
      return;
    }
  }
}
