#include <bits/stdc++.h>
using namespace std;
unsigned long long min(unsigned long long x, unsigned long long y) {
  if (x < y) return x;
  return y;
}
unsigned long long max(unsigned long long x, unsigned long long y) {
  if (x < y) return y;
  return x;
}
long long min(long long x, long long y) {
  if (x < y) return x;
  return y;
}
long long max(long long x, long long y) {
  if (x < y) return y;
  return x;
}
double min(double x, double y) {
  if (x < y) return x;
  return y;
}
double max(double x, double y) {
  if (x < y) return y;
  return x;
}
unsigned long long gcd(unsigned long long x, unsigned long long y) {
  if (!x) return y;
  if (!y) return x;
  if (x > y) swap(x, y);
  return gcd(x, y % x);
}
unsigned long long inv(unsigned long long a, unsigned long long c) {
  if (a == 1) {
    return 1;
  }
  return ((c - (c / a)) * inv(c % a, c)) % c;
}
int n, a, c[100005] = {0}, numa = 0;
unordered_set<int> cols;
map<int, int> cnts;
int main() {
  ios_base::sync_with_stdio(false);
  cin.tie(NULL);
  cout.tie(NULL);
  cin >> n >> a;
  for (int i = 0; i < n; i++) {
    cin >> c[i];
    if (c[i] != a) cols.insert(c[i]);
    cnts[c[i]]++;
  }
  for (int i = n - 1; i >= 0; i--) {
    if (c[i] == a) {
      vector<int> rem;
      for (unordered_set<int>::iterator it = cols.begin(); it != cols.end();
           ++it) {
        if (cnts[*it] < cnts[a]) rem.push_back(*it);
      }
      for (int i = 0; i < rem.size(); i++) {
        cols.erase(rem[i]);
      }
    }
    cnts[c[i]]--;
  }
  if (cols.empty())
    cout << "-1\n";
  else
    cout << (*cols.begin()) << "\n";
  return 0;
}
