In a survey, 51 American tourists were asked if they had visited the following Latin American countries: Argentina, Brazil and Columbia. The following facts were gathered. 35 had visited Argentina, 34 had visited Brazil and 19 had visited Columbia. 11 tourists had visited Argentina and Brazil and but not Columbia, 5 had visited Argentina and Columbia and not Brazil, 12 had visited Brazil, Argentina and Columbia. Everyone who visited Columbia also visited at least one of the following two countries: Argentina and Brazil. How many American tourists visited none of these countries Argentina, Brazil and Columbia?