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#include <bits/stdc++.h>
using namespace std;



typedef long long ll;
#define x first
#define y second
#define Exit(x) { x; return; }
#define debug(a, b) '(' << a << " = " << b << ')'
ll gll() { ll x; return cin >> x, x; }
int gint() { int x; return cin >> x, x; }
string gstr() { string x; return cin >> x, x; }
struct custom_hash {
    static uint64_t splitmix64(uint64_t x) {
        x += 0x9e3779b97f4a7c15;
        x = (x ^ (x >> 30)) * 0xbf58476d1ce4e5b9;
        x = (x ^ (x >> 27)) * 0x94d049bb133111eb;
        return x ^ (x >> 31);
    }

    size_t operator()(uint64_t x) const {
        static const uint64_t FIXED_RANDOM = chrono::steady_clock::now().time_since_epoch().count();
        return splitmix64(x + FIXED_RANDOM);
    }
};



        /* ------- declaration ------- */

    int x;
    unordered_map<int, bool, custom_hash> m;

/* ------- ~~~~~~~~~~~ ------- */



        /* ----------------- main func ----------------- */

    void query() {
        for (; cin >> x; m[x] = true)
            if (m[x]) Exit(cout << x);
    }

/* ----------------- ~~~~~~~~~ ----------------- */



int main(){
    //freopen("Test.INP", "r", stdin);
    //freopen("Test.OUT", "w", stdout);
    cin.tie(NULL)->sync_with_stdio(false);

        /* ------- setup ------- */

    srand(time(0));
    cout << fixed << setprecision(2);
    int t = 1; for (; t--; query());

/* ------- ~~~~~ ------- */

    return 0;
}



        /* ------- ~~~~~~~ -------



------- ~~~~~~~ ------- */