by an EU citizen. Similarly, although by law heads of state are not to receive a passport stamp, in practice, this is not always followed. For example, when arriving for the 37th G8 summit in Deauville, United States President Barack Obama had his passport stamped at Deauville – Saint-Gatien Airport. Similarly, when President Obama attended the 2009 Strasbourg–Kehl summit, his diplomatic passport was stamped on arrival at Strasbourg Airport on 3 April 2009, and after visiting Prague, Czech Republic, his diplomatic passport was stamped on departure from Prague Ruzyně Airport on 5 April 2009. Although, according to EU rules, third country nationals who hold residence permits should not have their travel documents stamped, France nevertheless requires third country nationals holding a visa de long séjour valant titre de séjour (a long-stay visa serving additionally as a residence permit for up to one year) to receive a passport stamp upon their first entry to the Schengen Area as a part of the process to validate the visa as a residence permit; without an entry stamp, the process cannot be completed. Third-country nationals who otherwise fulfil all the criteria for admission into the Schengen area must not be denied entry for the sole reason that there is no remaining empty space in their travel document to affix a stamp; instead, the stamp should be affixed on a separate sheet of paper. Entry and exit stamps are applied in black ink, except for the red date stamp and a two-digit security code in the middle. The two-digit security code must be changed at least once a month, although some Schengen countries (such as Greece) change security codes every day. The stamps bear the country abbreviation within a circle of stars in the top left hand corner, the name of the entry/exit border crossing point in Latin alphabet at the bottom, and an icon in the top right hand corner to denote the mode of entry/exit. Below the name of the border crossing point is an identifying number – a record is kept of the identity of the border officer to whom a given stamp is assigned at any given time. Entry stamps are rectangular and have an arrow into a square, while exit stamps are rectangular with rounded corners and have an arrow out of a square. The stamps do not indicate any maximum permitted duration of stay. Border guards are required to