#include<stdio.h>

int main(){
  int a,b,c,d;
  int count = 1;
  scanf("%d %d %d %d",&a,&b,&c,&d);
  do{
    if( count % 2 == 1 ){
      c = c - b;
    }else{
      a = a - d;
    }
    count++;
  }while( a <= 0 || c <= 0 );

  if( a > c ){
    printf("Yes\n");
  }else{
    printf("No\n");
  }

  return 0;
}