import sys,random,bisect
from collections import deque,defaultdict
import heapq
from itertools import permutations
from math import gcd

input = lambda :sys.stdin.readline().rstrip()
mi = lambda :map(int,input().split())
li = lambda :list(mi())

class SegmentTree:
    def __init__(self, init_val, segfunc, ide_ele):
        n = len(init_val)
        self.segfunc = segfunc
        self.ide_ele = ide_ele
        self.num = 1 << (n - 1).bit_length()
        self.tree = [ide_ele] * 2 * self.num
        self.size = n
        for i in range(n):
            self.tree[self.num + i] = init_val[i]
        for i in range(self.num - 1, 0, -1):
            self.tree[i] = self.segfunc(self.tree[2 * i], self.tree[2 * i + 1])

    def update(self, k, x):
        k += self.num
        self.tree[k] = x
        while k > 1:
            k >>= 1
            self.tree[k] = self.segfunc(self.tree[2*k], self.tree[2*k+1])

    def query(self, l, r):
        if r==self.size:
            r = self.num

        res = self.ide_ele

        l += self.num
        r += self.num
        right = []
        while l < r:
            if l & 1:
                res = self.segfunc(res, self.tree[l])
                l += 1
            if r & 1:
                right.append(self.tree[r-1])
            l >>= 1
            r >>= 1

        for e in right[::-1]:
            res = self.segfunc(res,e)
        return res

    def bisect(self,l,r,x):
        if r==self.size:
            r = self.num
        l += self.num
        r += self.num
        segment = []
        segment_r = []
        while l<r:
            if l&1:
                segment.append(l)
                l += 1
            if r&1:
                segment_r.append(r-1)
            l >>= 1
            r >>= 1
        segment += segment_r[::-1]
        tmp = 0
        for pos in segment:
            check = tmp + self.tree[pos]
            if check >= x:
                break
            else:
                tmp = check
        else:
            return -1
        
        while pos < self.num:
            check = tmp + self.tree[2*pos]
            if check >= x:
                pos = 2 * pos
            else:
                tmp = check
                pos = 2 * pos + 1
        return pos - self.num

ACGT = [0,2,6,19]

N = int(input())
S = input()
S = [ord(s)-ord("A") for s in S]

cnt = [0] * 26
for a in S:
    cnt[a] += 1

res = 0
tmp = 0
seg = SegmentTree([1]*N,lambda x,y:x+y,0)
while True:
    k = 0
    for i in ACGT:
        k += cnt[(i-tmp)%26]
    if k==0:
        break
    i = seg.bisect(0,N,k)
    assert i!=-1
    seg.update(i,0)
    res += 1
    cnt[S[i]] -= 1
    tmp += cnt[S[i]]
    tmp %= 26

print(res)