#include <stdio.h>
#include <stdlib.h>
#include <math.h>

int max (int a, int b) {
    if (a > b) return a;
    else return b;
}

int main(){
    int i, *diff_2, *diff_1, * duck, n, diff, start;

    while (1) {
        if (scanf("%i", &n) != 1) break;
        duck = malloc(sizeof(int)* n);
        diff_1 = malloc(sizeof(int)* n);
        diff_2 = malloc(sizeof(int)* n);
        for (i = 0; i < n; i++) scanf("%i", &duck[i]);

        for(i = 0; i < n; i++){
            diff_2[i] = 0;
        }
        for (i = 0; i < n - 1; i++){
            if (duck[i] == duck[i + 1]){
                diff_1[i] = 1;
            } else {
                diff_1[i] = 0;
            }
        }

        diff_1[n - 1] = 0;

        for (diff = 2; diff < n; diff++){
            for (start = 0; (start + diff) < n; start++){
                if (duck[start] == duck[start + diff]){
                    diff_2[start] = diff_1[start];
                    diff_1[start] = diff_2[start + 1] + 1;
                } else {
                    diff_2[start] = diff_1[start];
                    diff_1[start] = max(diff_1[start], diff_1[start + 1]);
                }
            }

        }
        printf("%i\n", diff_1[0]);



        free(duck);
        free(diff_1);
        free(diff_2);

    }

    return 0;
}