// https://www.acmicpc.net/problem/1695

// 부분 수열을 팰린드롬을 만들때 끼워넣는 최소 개수

public static void main(String[] args) throws IOException {

BufferedReader br = new BufferedReader(new InputStreamReader(System.in));

int n = Integer.parseInt(br.readLine());

int[] arr = new int[n + 1];

int[][] dy = new int[n + 1][n + 1];

StringTokenizer st = new StringTokenizer(br.readLine());

for (int i = 1; i <= n; i++) {

arr[i] = Integer.parseInt(st.nextToken());

}

for (int i = 1; i < n; i++) {

for (int j = 1; j <= n-1 ; j++) {

if(arr[j] == arr[j+i]) dy[j][j + 1] = dy[j + 1][j + 1 - 1];

else dy[j][j + 1] = Math.min(dy[j + 1][j + 1], dy[j][j + i - 1]) + 1;

}

}

System.out.println(dy[1][n]);

}