#include <bits/stdc++.h>

using namespace std;
vector<int> c;
int n;
int isCorrect(int el, int indTo, int indFrom) {
	for(int k = indFrom; k >indTo; k--) {
		if(c[k] == el) {
			return k;
		}
	}
	return -1;
}

int main() {
	int max;
	ios::sync_with_stdio(false);

	while(scanf("%d", &n) == 1) {
		max = 0;
		c.clear();
		c.resize(n);
		for(int i = 0; i < n; i++) {
			scanf("%d",&c[i]);
		}
		int el,sz,indFrom,ind;
		for(int i = 0; i < n; i++) {
			sz = 0, indFrom = n-1;
			for(int j = i; j < n; j++) {
				el = c[j];
				ind = isCorrect(el,j,indFrom);
				if(ind>-1) { sz++; indFrom = ind;}			
			}
			if(sz > max) max = sz;
			
		}
		cout << max << endl;
	}
	return 0;
}