Given a string S₀S₁ … S_L-1S_LS_L+1 … S_{2L-1，the different value means the number of different characters between} S₀S₁ … S_{L-1 and} S_LS_L+1 … S_{2L-1, when compare them from left to right. For example, different value of abcaec is 1,because only the second character is different between abc and aec.}

    _{Now,given a string, you should find out that whether it contains a substring of even length, of which the different value is not bigger than a given value D. If you can find more than one substrings matching condition, please output the longest one. If more than one substrings of same length match condition, please output the one nearest from the left end.}

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NYOJ