uses crt;
var n,i,k:integer;
snt:boolean;
begin
clrscr;
write('Nhap n:');readln(n);
snt := true;
if n<=1 then snt:=false;
if n>=2 then
for i:=2 to trunc(sqrt(n)) do
if n mod i=0 then snt:=false;
if snt=true then write('So nguyen to') else write('Khong phai so nguyen to');
readln
end.