CREATE TABLE table_64744 ("Rank" TEXT, "Province" TEXT, "Population  ( 2011 ) " FLOAT, "Percentage" FLOAT, "Population Estimate  ( 2013 ) " FLOAT)

What is the lowest 2013 population estimate of south africa, which has a percentage greater than 19.8 and a 2011 population greater than 51,770,561?
SELECT MIN("Population Estimate (2013)") FROM table_64744 WHERE "Percentage" > '19.8' AND "Province" = 'south africa' AND "Population (2011)" > '51,770,561'
SELECT MIN("Population Estimate (2013)") FROM "table_64744" WHERE "Percentage" > '19.8' AND "Population (2011)" > '51,770,561' AND "Province" = 'south africa'