#include <bits/stdc++.h>
using namespace std;
const long long INF = 1e18 + 5;
const int mod = 1e9 + 7;
const int N = 3 * 1e5 + 5;
int n, c[N], maxOf[N];
int main() {
  ios_base::sync_with_stdio(false);
  cin >> n;
  for (int i = 0; i < n; i++) {
    cin >> c[i];
    maxOf[c[i]] = i;
  }
  int last = c[n - 1];
  int bb = -1;
  for (int i = n - 1; i >= 0; i--) {
    if (c[i] != last) {
      bb = i;
      break;
    }
  }
  assert(bb != -1);
  int ans = 0;
  for (int i = 0; i < n; i++) {
    if (c[i] != last) {
      ans = max(ans, n - 1 - i);
    } else {
      ans = max(ans, bb - i);
    }
  }
  cout << ans << endl;
  return 0;
}
