#!/usr/bin/env PyPy3

from collections import Counter, defaultdict, deque
import itertools
import re
import math
from functools import reduce
import operator
import bisect
from heapq import *
import functools
mod=998244353

import sys
input=sys.stdin.readline
n = int(input())
s = input().rstrip()
cnt = 0
for i in range(n):
    if s[i] == 'A' or s[i] == 'G' or s[i] == 'C' or s[i] == 'T':
        cnt += 1
ans = 0
now = cnt
while cnt:
    if s[now-1] == 'A' or s[now-1] == 'G' or s[now-1] == 'C' or s[now-1] == 'T':
        cnt -= 1
        now = cnt
    else:
        now = cnt + ans + 1
    ans += 1
print(ans)