#include <iostream>
#include <string>
#include <cstring>
#include <map>
using namespace std;
const int maxn = 205;
map<pair<char, char>, bool> compatible;
int dp[maxn][maxn];
string s;
int rec(int i, int j) {
    if(j - i <= 1) {
        return 0;
    }
    if(dp[i][j] != -1) {
        return dp[i][j];
    }
    int res = 0;
    if(compatible[make_pair(s[i], s[j])]) {
        res = max(res, rec(i + 1, j - 1) + 1);
    }
    for(int k = i; k < j; k++) {
        res = max(res, rec(i, k) + rec(k + 1, j));
    }
    return dp[i][j] = res;
}
int main() {
    ios_base::sync_with_stdio(false);
    int n;
    cin >> n;
    cin >> s;

    compatible[make_pair('A', 'U')] = true;
    compatible[make_pair('U', 'A')] = true;
    compatible[make_pair('C', 'G')] = true;
    compatible[make_pair('G', 'C')] = true;
    compatible[make_pair('G', 'U')] = true;
    compatible[make_pair('U', 'G')] = true;
    memset(dp, -1, sizeof dp);

    cout << rec(0, n - 1) << endl;
    return 0;
}