rank nation gold silver bronze total
rank
nation
gold
silver
bronze
total
number
number
number
number
number
number text number number number number
1 venezuela 5 2 3 10
how many nations won at least three silver medals ?
WRB JJ NNS VBD IN JJS CD JJ NNS .
5
select count ( c2 ) from w where c4_number >= 3