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

void main() {
  int a, b, c, d;
  readf("%d %d %d %d\n", &a, &b, &c, &d);
  while(true) {
    c -= b;
    if(c<=0) {
      writeln("Yes");
      return;
    }
    a -= d;
    if(a<=0) {
      writeln("No");
      return;
    }
  }
}
