#include <bits/stdc++.h>
using namespace std;
const int maxn = 5005;
int dp[maxn][maxn][2], n, c[maxn];

int main() {
    cin >> n;
    for (int i = 1; i <= n; i++) cin >> c[i];
    for (int l = 1; l <= n; l++) {
        for (int i = 1; i+l-1 <= n; i++) {
            int j = i+l-1;
            if (l == 1) dp[i][j][0] = dp[i][j][1] = 0;
            else {
                dp[i][j][0] = min( dp[i+1][j][0] + (c[i] != c[i+1]) , dp[i+1][j][1] + (c[i] != c[j]) );
                dp[i][j][1] = min( dp[i][j-1][0] + (c[i] != c[j]) , dp[i][j-1][1] + (c[j-1] != c[j]) );
            }
        }
    }
    cout << min(dp[1][n][0], dp[1][n][1]) << endl;
    return 0;
}