const str1=readline() let arr =str1.split("") let str="" let tem=[] tem.push(arr[0]) var iss=(str)=>{ let flag=true for(let i=0;i<Math.ceil((str.length)/2);i++){ if(str[i]!==str[[str.length-1]-i]) flag= false } return flag } for(let i=0;i<arr.length;i++){ for(let j=i+1;j<arr.length;j++){ if(iss(str1.substring(i,j+1))){ tem.push(str1.substring(i,j+1)) } } } let max=0 let s="" tem.forEach((i,index)=>{ let curr=i.length if(curr>=max){ max=curr s=i } })