#include<stdio.h>

int main(void){

int a,b,c,d;

scanf("%d %d %d %d",&a,&b,&c,&d);

while(1){
c = c - b;
a = a - d;
if(c <= 0){
  printf("Yes\n");
  break;
}else if(a <= 0){
    printf("No\n");
    break;
}

}

return 0;
}
