var p:longint;
x,i,j,k,n,s,d:integer;
f,g:text;
begin
assign(f,'factoriale.in');reset(f);
assign(g,'factoriale.out');rewrite(g);
read(f,n,k);
p:=1;
for i:=1 to n do begin
read(f,x);
for j:=2 to x do
p:=p*j;
end;
if trunc(sqrt(p*2))=sqrt(p*2) then writeln(g,'2')
                              else begin
d:=3;
s:=d;
while int(sqrt(p*d))<>sqrt(p*d) do begin
p:=p*d;
s:=d;
d:=d+2;
end;
write(g,s);
end;
close(f);
close(g);
end.