#include <stdio.h>

int main(){
  int A,B,C,D;
  scanf("%d %d %d %d",&A,&B,&C,&D);
  int turn=1;
    while(A > 0 && C > 0){
      if(turn== 1){
      C=C-B;
      }else if(turn == -1){
      A=A-D;
    }
      turn=-turn;
    }
  if(A>0){
    printf("Yes\n");
  }else{
    printf("No\n");
  }
  return 0;
}