#include <bits/stdc++.h>

using namespace std;

#define fr(a,b,c) for(int (a) = (b); (a) < (c); ++(a))
#define rp(a,b) fr(a,0,b)
#define fre(a,b) for(int a = adj[b]; ~a; a = ant[a])
#define cl(a,b) memset((a), (b), sizeof(a))
#define sc(a) scanf("%d", &a)
#define sc2(a,b) scanf("%d%d", &a, &b)
#define sc3(a,b,c) scanf("%d%d%d", &a, &b, &c)
#define scs(s) scanf("%s", s)
#define pri(x) printf("%d\n", x)

#define iter(a) __typeof((a).begin())
#define fore(a,b) for(iter(b) a = (b).begin(); a != (b).end(); ++a)

#define st first
#define nd second
#define mp make_pair
#define pb push_back

#define db(x) cerr << #x << " == " << x << endl
#define dbs(x) cerr << x << endl
#define _ << ", " <<

const int oo = 0x3f3f3f3f;

typedef long long ll;
typedef pair<int,int> pii;
typedef vector<int> vi;
typedef vector< vi > vii;
typedef unsigned long long ull;

#define MOD 1000000007

char str[100010];
int n;
unordered_set<int> s;

bool test(int x) {
    s.clear();
    rp(i,n-x+1) {
        int h = 0;
        fr(j,i,i+x) {
            h = ((h<<1) + (str[j] == '-'))%MOD;
        }
        if (s.count(h)) return true;
        s.insert(h);
    }
    return false;
}

void proc(int x) {
    s.clear();
    rp(i,n-x+1) {
        int h = 0;
        fr(j,i,i+x) {
            h = ((h<<1) + (str[j] == '-'))%MOD;
        }
        if (s.count(h)) {
            fr(j,i,i+x) {
                printf("%c", str[j]);
            }
            puts("");
            return;
        }
        s.insert(h);
    }
}

int main() {
    scs(str);
    n = strlen(str);
    int ini = 0, fim = n;
    while (ini < fim) {
        int m = (ini+fim+1)>>1;
        if (test(m)) ini = m;
        else fim = m-1;
    }
    if (ini < 3) puts("*");
    else proc(ini);
}