#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);
    while(1){
    rep(i,s.size()){
        rep(j,4){
            c+=s[i]==t[j];
        }
    }
    if(c==0) break;
    s.erase(c-1,1);
    c=0;
    cnt++;
    }
    out(cnt,endl);

    return 0;
}