String c = "";
for (int n=0; n <4; n++){

for (int i=0; i < a.length(); i++){
  char d = a.charAt(i);
  if (d == 'X'){
  c = c + "X+YF++YF-FX--FXFX-YF+";
  }
  else if (d=='Y'){
    c = c + "-FX+YFYF++YF+FX--FX-Y";
  }
  else c = c + d;
}
a=c;
}

for (int i=0; i < c.length(); i++){
  char b = c.charAt(i);
  if (b == '+'){

  angle = angle + radians(60);
  }
  if(b == '-'){
  angle = angle + radians(300);
  }
  if (b=='F'){

    px2=px1 + 5*cos(angle);
    py2=py1 + 5*sin(angle);
    line(px1,py1,px2,py2);
    px1=px2;
    py1=py2;

  }
}
}