program duplicato;
const MAXN=100000;
      MAXP=10000000;
var N,i:longint;
    duplicatomancante, massimo :int64;
    P  : array[1..2*MAXN] of longint;
    duplicati : array[1..MAXP] of longint;
begin
       (* assign(input, 'input.txt'); reset(input);
        assign(output, 'output.txt'); rewrite(output);*)
	readln(N);
        massimo:=0;
        for i:=1 to  2*N-1 do  begin read(P[i]); if P[i]>massimo then massimo:=P[i]; end;
        for i:=1 to  massimo do duplicati[i]:=0;        
	for i:=1 to  massimo do begin duplicati[P[i]]:=duplicati[P[i]]+1;end;
	for i:=1 to massimo do if duplicati[i]=1 then duplicatomancante:=i;
	writeln (duplicatomancante);
end.

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