CODEFORCE 126B Password

#include <cstdio>
#include <iostream>
#include <algorithm>
#include <cstring>
#include <cmath>
#include <queue>
#include <vector>
using namespace std;

#define N 1000010

int n,f
,Ans;
char S
;

void Solve()
{
n=(int)strlen(S);
f[0]=0;f[1]=0;
for(int i=1;i<n;i++)
{
int j=f[i];
while(j&&S[j]!=S[i])
j=f[j];
if(S[j]==S[i])
f[i+1]=j+1;
else f[i+1]=0;
}
for(int i=1;i<=n;i++)
{
if(i!=n)
Ans=max(Ans,f[i]);
else
{
int now=f[i];
if(now>Ans)
now=f[now];
Ans=now;
}
}
if(Ans==0)
{
cout<<"Just a legend"<<endl;
return;
}
for(int i=0;i<Ans;i++)
printf("%c",S[i]);
cout<<endl;
}

int main()
{
scanf("%s",S);
Solve();
return 0;
}