class Bit:
    def __init__(self, n):
        self.size = n
        self.n0 = 1 << (n.bit_length() - 1)
        self.tree = [0] * (n + 1)
    
    def range_sum(self, l, r):
        return self.sum(r - 1) - self.sum(l - 1)
        
    def sum(self, i):
        i += 1
        s = 0
        while i > 0:
            s += self.tree[i]
            i -= i & -i
        return s
        
    def get(self, i):
        return self.sum(i) - self.sum(i - 1)
 
    def add(self, i, x):
        i += 1
        while i <= self.size:
            self.tree[i] += x
            i += i & -i
         
    def lower_bound(self, x):
        pos = 0
        plus = self.n0
        tot = 0
        while plus > 0:
            if pos + plus <= self.size and self.tree[pos + plus] < x:
                x -= self.tree[pos + plus]
                pos += plus
            plus //= 2
        return pos

def stupid(S):
    ret = 0
    while 1:
        cnt = 0
        for s in S:
            if s in "AGCT":
                cnt += 1
        if cnt == 0:
            break
        ret += 1
        T = S[:cnt - 1] + S[cnt:]
        s = S[cnt - 1]
        cnt2 = 0
        for t in T:
            if t == s:
                cnt2 += 1
        S = []
        for s in T:
            p = ord(s) - 65
            p += cnt2
            p %= 26
            S.append(chr(p + 65))
        S = "".join(S)

    return ret

def solve(S):
    n = len(S)
    bit = Bit(n)
    for i in range(n):
        bit.add(i, 1)
    cnt = [0] * 26
    S = [ord(s) - 65 for s in S]
    for s in S:
        cnt[s] += 1
    rot = 0
    agct = [0, 6, 2, 19]
    ret = 0
    while 1:
        c1 = 0
        for i in agct:
            c1 += cnt[(i - rot) % 26]
        if c1 == 0:
            break
        ret += 1
        p = bit.lower_bound(c1)
        bit.add(p, -1)
        cnt[S[p]] -= 1
        c2 = cnt[S[p]]
        rot += c2
        
        
    return ret


n = int(input())
S = input()
print(solve(S))