import java.io.*;
import java.util.*;

public class floodFill {

	static final boolean stdin = true;
	static final String filename = "";
	static FastScanner br;
	static PrintWriter pw;

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

		if (stdin) {
			br = new FastScanner();
			pw = new PrintWriter(new OutputStreamWriter(System.out));
		}

		else {
			br = new FastScanner(filename + ".in");
			pw = new PrintWriter(new FileWriter(filename + ".out"));
		}

		X solver = new X();
		solver.solve(br, pw);
	}

	static class X {
		public void solve(FastScanner br, PrintWriter pw) throws IOException {
			int N = br.nextInt();

			int[] a = new int[N];

			for(int i = 0; i < N; i++) {
				a[i] = br.nextInt();
			}

			int[][][] dp = new int[N][N][2]; //dp[i][j][0] = using left, dp[i][j][1] = using right

			for(int i = 0; i < N; i++) {
				for(int j = 0; j < N; j++) {
					dp[i][j][0] = dp[i][j][1] = Integer.MAX_VALUE;
				}
			}

			for(int i = 0; i < N; i++) {
				dp[i][i][0] = dp[i][i][1] = 0;
			}

			for(int l = 1; l <= N; l++) {
				for(int s = 0; s < N; s++) {

					if(s + l >= N) {
						continue;
					}

					if(a[s] == a[s+1]) {
						dp[s][s+l][0] = Math.min(Math.min(dp[s][s+l][0],dp[s+1][s+l][1]+1),dp[s+1][s+l][0]);
					}
					else if(a[s] == a[s+l]) {
						dp[s][s+l][1] = Math.min(Math.min(dp[s][s+l][1], dp[s][s+l][1]), dp[s][s+l][0]+1);
					}
					if(a[s+l] == a[s+l-1]) {
						dp[s][s+l][1] = Math.min(dp[s][s+l][1], Math.min(dp[s][s+l-1][1], dp[s][s+l-1][0]+1));
					}
					else if(a[s+l] == a[s]) {
						dp[s][s+l][0] = Math.min(dp[s][s+l][0], Math.min(dp[s][s+l-1][0], dp[s][s+l-1][1]+1));
					}

					dp[s][s+l][0] = Math.min(dp[s][s+l][0], (Math.min(dp[s+1][s+l][0], Math.min(dp[s+1][s+l][1], Math.min(dp[s][s+l-1][0], dp[s][s+l-1][1]))))+1);
					dp[s][s+l][1] = Math.min(dp[s][s+l][1], Math.min(dp[s+1][s+l][0], Math.min(dp[s+1][s+l][1], Math.min(dp[s][s+l-1][0], dp[s][s+l-1][1])))+1);


				}


			}

			pw.println(Math.min(dp[0][N-1][0],dp[0][N-1][1]));


			pw.close();
		}

	}

	//fastscanner class
	public static class FastScanner {
		BufferedReader br;
		StringTokenizer st;

		public FastScanner(String s) {
			try {
				br = new BufferedReader(new FileReader(s));
			} catch (FileNotFoundException e) {
				// TODO Auto-generated catch block
				e.printStackTrace();
			}
		}

		public FastScanner() {
			br = new BufferedReader(new InputStreamReader(System.in));
		}

		String nextToken() {
			while (st == null || !st.hasMoreElements()) {
				try {
					st = new StringTokenizer(br.readLine());
				} catch (IOException e) {
					// TODO Auto-generated catch block
					e.printStackTrace();
				}
			}
			return st.nextToken();
		}

		int nextInt() {
			return Integer.parseInt(nextToken());
		}

		long nextLong() {
			return Long.parseLong(nextToken());
		}

		double nextDouble() {
			return Double.parseDouble(nextToken());
		}
	}

}