program exe;

var n,i,s,j:integer;

a,b:array[1..1000]of integer;

begin

read(n);s:=0;

for i:=1 to n do read(a[i]);

for i:=1 to n do b[i]:=0;

for i:=1 to n do

for j:=1 to n do

if a[i]=a[j] then b[i]:=b[i]+1;

for i:=1 to n do if b[i]=1 then s:=a[i];

write(s);

end.