#include <fstream>
#include <iostream>
using namespace std;
int main() {
ifstream fin("bac.txt");
int ok = 0;
int x, y, aparitii = 0;
fin >> x;
aparitii = 1;
y = x;
while (fin >> x) {
if (x == y)
aparitii++;
else {
if (aparitii % 2 == 1) {
ok = 1;
cout << y << "\n";
break;
}
y = x;
aparitii = 1;
}
}
if (!ok)
cout << "nu exista\n";
return 0;
}