#include <bits/stdc++.h>
using namespace std;
const int INF = 1 << 30;
const long long int MAX = 1e9 + 7;
void array_show(int *array, int array_n, char middle = ' ') {
  for (int i = 0; i < array_n; i++)
    printf("%d%c", array[i], (i != array_n - 1 ? middle : '\n'));
}
void array_show(long long int *array, int array_n, char middle = ' ') {
  for (int i = 0; i < array_n; i++)
    printf("%lld%c", array[i], (i != array_n - 1 ? middle : '\n'));
}
void array_show(vector<int> &vec_s, int vec_n = -1, char middle = ' ') {
  if (vec_n == -1) vec_n = vec_s.size();
  for (int i = 0; i < vec_n; i++)
    printf("%d%c", vec_s[i], (i != vec_n - 1 ? middle : '\n'));
}
void array_show(vector<long long int> &vec_s, int vec_n = -1,
                char middle = ' ') {
  if (vec_n == -1) vec_n = vec_s.size();
  for (int i = 0; i < vec_n; i++)
    printf("%lld%c", vec_s[i], (i != vec_n - 1 ? middle : '\n'));
}
int t[110000];
int num[1100000];
int main() {
  int n, m;
  int i, j, k;
  int a, b, c;
  cin >> n >> m;
  int cnt = 0;
  for (i = 0; i < n; i++) {
    cin >> t[i];
  }
  for (i = n - 1; i >= 0; i--) {
    if (t[i] == m) {
      cnt++;
      continue;
    }
    if (num[t[i]] < cnt) num[t[i]]++;
  }
  for (i = 1; i <= 1e6; i++) {
    if (i == m) continue;
    if (num[i] >= cnt) {
      cout << i << endl;
      return 0;
    }
  }
  cout << -1 << endl;
}
