#pragma GCC optimize("Ofast,unroll-loops")
#include <bits/stdc++.h>
using namespace std;

#ifdef WAIMAI
#define debug(HEHE...) cout<<"["<<#HEHE<<"] : ",dout(HEHE)
void dout(){cout<<'\n';}
template<typename T,typename...U>
void dout(T t,U...u){cout<<t<<(sizeof...(u)?", ":""),dout(u...);}
#else
#define debug(...) 7122
#endif

#define int long long
#define ll long long
#define Waimai ios::sync_with_stdio(false),cin.tie(0)
#define FOR(x,a,b) for(int x=a,I=b;x<=I;x++)
#define pb emplace_back
#define F first
#define S second

const int INF = 1e9;
const int base = 137;
const int MOD = 1e9 + 7;
const int SIZE = 3e5 + 5;

int n, mn;
string s;
int pro[SIZE], inv[SIZE], pre[SIZE];

int hs (int l, int r) {
    int x = (pre[r] - pre[l - 1]) * inv[l - 1] % MOD;
    return x < 0 ? x + MOD : x;
}

bool ok (int len) {
    unordered_map<int, pair<int, int>> mp;
    FOR (i, 1, n - len + 1) {
        int val = hs (i, i + len - 1);
        mp[val].F = i;
        mp[val].S++;
    }
    mn = INF;
    for (auto [x, c] : mp) if (c.S == 1) mn = min (mn, c.F);
    return mn != INF;
}

int power (int d, int up) {
    int re = 1;
    while (up) {
        if (up & 1) re = re * d % MOD;
        d = d * d % MOD;
        up >>= 1;
    }
    return re;
}

void solve() {
    cin >> s;
    n = s.size();
    s = " " + s;

    pro[0] = inv[0] = 1;
    inv[1] = power (base, MOD - 2);
    FOR (i, 1, n) {
        pro[i] = pro[i - 1] * base % MOD;
        inv[i] = inv[i - 1] * inv[1] % MOD;
        pre[i] = (pre[i - 1] + s[i] * pro[i]) % MOD;
    }

    int l = 1, r = n;
    while (l < r) {
        int mid = (l + r) / 2;
        if (ok (mid)) r = mid;
        else l = mid + 1;
    }
    ok (l);
    cout << s.substr (mn, l) << '\n';
}

int32_t main() {
    Waimai;
	solve();
}