#include<stdio.h>
#define rep(i,a,b) for(int i = a;i <= b;i++)

int main(void){
  int a,b,c,d; scanf("%d%d%d%d",&a,&b,&c,&d);
  rep(i,1,200){
    if(i%2!=0){
      c -= b;
      if(c <= 0){
        printf("Yes");
        break;
      }
    }
    else{
      a -= d;
      if(a <= 0){
        printf("No");
        break;
      }
    }
  }

  return 0;
}
