#include <iostream>
#include <vector>
#include <string>
#include <algorithm>
#include <cmath>

#define rep(i,n) for(i=0; i<n; ++i)
#define in(a) cin >> a
#define out(a,b) cout << a << b
using namespace std;
using lint = long long;

int main(void){
    int i, j, k, y, n, cnt=0, sum=0,c=0;
    in(n);
    string s, t="AGCT";
    in(s);
    vector<bool> x(n,true);
    while(1){
    rep(i,n){
        rep(j,4){
            if(s[i]==t[j]&&x[i]){
            c++;
            }
        }
    }
    if(c==0) break;
    //x[c-1]=false;
    rep(i,n){
        if(x[i]) sum++;
        if(sum == c) {x[i]=false;
        break;}
    }
    sum=0;
    c=0;
    cnt++;
    }
    out(cnt,endl);

    return 0;
}