C++ :

#include<iostream>
#include<cstdio>
#include<cstring>
#include<algorithm>
#define ull unsigned long long
using namespace std;

const int N=1e6+10;
const int base=131;

char str[2*N];
ull hl[2*N],hr[2*N],p[2*N];

ull get(ull h[],int l,int r)
{
    return h[r]-h[l-1]*p[r-l+1];
}

int main()
{
    int T=1;
    while(~scanf("%s",str+1),strcmp("END",str+1))
    {
        ///添加'{'符号
        int n=strlen(str+1);
        for(int i=2*n;i;i-=2)
        {
            str[i]=str[i/2];
            str[i-1]='z'+1;
        }
        ///长度增大
        n*=2;

        p[0]=1;
        for(int i=1,j=n;i<=n;i++,j--)
        {
            hl[i]=hl[i-1]*base+str[i]-'a'+1;
            hr[i]=hr[i-1]*base+str[j]-'a'+1;
            p[i]=p[i-1]*base;
        }

        int res=0;
        for(int i=1;i<=n;i++)
        {
            int l=0,r=min(i-1,n-i);
            while(l<r)
            {
                int mid=l+r+1>>1;
                ///hl左端点i-mid,右端点i-1；hr左端点要翻转
                if(get(hl,i-mid,i-1)!=get(hr,n-(i+mid)+1,n-(i+1)+1)) r=mid-1;
                else l=mid; ///mid=l+r+1>>1
            }

            ///字母多一个，回文半径是l，总长度为2l+1
            if(str[i-l]<='z') res=max(res,(2*l+1)/2+1);///上取整
            else res=max(res,l);
        }

        printf("Case %d: %d\n",T++,res);
    }

    return 0;

}