program indexing;
var
A, B, C : AnsiString;
dimA, dimB,i, n :Longint;
begin
(*assign(input, 'input.txt'); reset(input);
assign(output, 'output.txt'); rewrite(output);*)
ReadLn(A);
ReadLn(B);
C := '';
dimA:=Length(A); dimB:=Length(B);
i:=1;
if (A[1]<>B[1]) and (dimA<>1) and (dimB<>1) then begin n:=ord(A[1]); C:=C+chr(n+1); end;
writeln(C);
end.
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