import java.io.BufferedReader import java.io.InputStream import java.io.InputStreamReader import java.io.PrintWriter import java.lang.StringBuilder import java.util.* fun PrintWriter.solve(sc: FastScanner) { val n = sc.nextInt() val a = Array(n) { sc.nextInt() - 1 } val segcount = Array(n) { 0 } val num = a.distinct().count() var color = a[0] for (i in 0 until n) { if (color != a[i]) { segcount[color]++ color = a[i] } if (i == n - 1 && color != a[0]) { segcount[color]++ } } if (segcount.any { it >= 2 }) { println(-1) } else if (a[0] == a[n - 1] && num >= 2) { println(1) } else { println(0) } } fun main() { val writer = PrintWriter(System.out, false) writer.solve(FastScanner(System.`in`)) writer.flush() } class FastScanner(s: InputStream) { private var st = StringTokenizer("") private val br = BufferedReader(InputStreamReader(s)) fun next(): String { while (!st.hasMoreTokens()) st = StringTokenizer(br.readLine()) return st.nextToken() } fun nextInt() = next().toInt() fun nextLong() = next().toLong() fun nextLine() = br.readLine() fun nextDouble() = next().toDouble() fun ready() = br.ready() }