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

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