program Hello;
var n, i, j:longint;
min: int64;
b:array[1..100000] of longint;
begin
min:= 99999999999999;
readln(n);
for i:= 1 to n do read(b[i]);
for i:= 1 to n do
for j:= i + 1 to n do
if b[i] < b[j] then
if min > b[i]*b[j] then
min:= b[i]*b[j];
if min = 99999999999999 then
writeln('khong co ket qua')
else
writeln(min);
readln;
readln;
end.