after wife tragic death Eurydice Orpheus descend realm death Reaching gate uneasy passing prove challenge mostly Cerberus threeheade hound Hades Orpheus famous poet musician plan calm Cerberus poetry safely walk past he create peculiar poem Cerberus it consist lowercase english letter we poem substre palindrome read backwards forwards a string substre string b obtain b delete possibly zero character begin possibly zero character endunfortunately Cerberus dislike palindrome length great 1 for example poem abaa hound Hades would not like substring aba aaOrpheus calm Cerberus hound like poetry that s want change poem contain palindrome substring length great 1orpheus modify poem replace letter position lowercase english letter he use operation arbitrarily time possibly zero since palindrome poem correction but exactly give poem determine minimal number letter change poem contain palindrome length great 1