uses crt;
var d,d2,n,i,j,nt: integer;
begin
clrscr;
    readln(n);
    for i:=1 to n do if n mod i = 0 then d:=d+1;
    if d<>2 then write(n,' khong la so nguyen to') else begin
        for i:=1 to n-1 do begin
                d:=0;
                for j:=1 to i do if i mod j = 0 then d:=d+1;
                if d=2 then begin
                    nt:=i;
                    d2:=1;
                end;
            end;
        if d2=0 then write('Khong co so nguyen to truoc ',n) else write('So nguyen to truoc ',n,' la: ',nt);
    end;
    readln
end.

n = int(input('N = '))
prime = [i for i in range (n+1)]
prime[0] = prime[1] = 0
for i in range (2,int(n**0.5)+1):
    for j in range (i**2,n+1,i):
        prime[j] = 0
if (n not in prime):
    print('N khong la so nguyen to')
else:
    print('N la so nguyen to')
    print('Cac so nguyen to lien truoc la:',*[i for i in prime[:-1] if i!=0])

$\color{red}{\text{#Daoanhviet96}}$