#include <stdio.h>
#include <math.h>

int main(){

  int A = 0, B = 0, C = 0, D = 0;
  scanf("%d %d %d %d", &A, &B, &C, &D);

  int res = 0;
  do{
    if( C - B <= 0 ){
      res = 1;
      break;
    }
    else{
      C = C - B;
    }
    if( A - D <= 0 ){
      break;
    }
    else{
      A = A - D;
    }
  } while(res < 10);

  if( res == 1 ){
    printf("Yes");
  }
  else{
    printf("No");
  }

  return 0;
}
