#include <iostream>
#include <map>
#include <cstring>
using namespace std;
string s;
int n;
map<pair<char, char>, bool> mapping;
int dp[222][222];
int rec(int i, int j) {
    if(j - i <= 1) {
        return 0;
    }
    if(dp[i][j] != -1) {
        return dp[i][j];
    }
    int result = 0;
    if(mapping[make_pair(s[i], s[j])]) {
        result = max(result, rec(i + 1, j - 1) + 1);
    }
    for(int k = i; k < j; k++) {
        result = max(result, rec(i, k) + rec(k + 1, j));
    }
    return dp[i][j] = result;
}
int main() {
    ios_base::sync_with_stdio(false);
    cin >> n >> s;
    mapping[make_pair('A', 'U')] = true;
    mapping[make_pair('U', 'A')] = true;
    mapping[make_pair('C', 'G')] = true;
    mapping[make_pair('G', 'C')] = true;
    mapping[make_pair('G', 'U')] = true;
    mapping[make_pair('U', 'G')] = true;
    memset(dp, -1, sizeof dp);
    cout << rec(0, n - 1) << endl;
     return 0;
}