#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, n, m, k, cnt = 0;
    string s, u="AGCT";
    char let;
    int c=0;
    in(n);
    in(s);
    rep(i,n){
        rep(j,4)    c+=s[i]==u[j];
    }
    while(c){
        cnt++;
        let = s[c-1];
        s.erase(c-1,1);
        rep(i,4)    c-=let==u[i];
    }
    out(cnt,endl);

    return 0;
}