#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;
}