## https://yukicoder.me/problems/no/1951

class BinaryIndexTree:
    """
    フェニック木(BinaryIndexTree)の基本的な機能を実装したクラス
    """
    def __init__(self, size):
        self.size = size
        self.array = [0] * (size + 1)
    
    def add(self, x, a):
        index = x
        while index <= self.size:
            self.array[index] += a
            index += index & (-index)
    
    def sum(self, x):
        index = x
        ans = 0
        while index > 0:
            ans += self.array[index]
            index -= index & (-index)
        return ans

    def least_upper_bound(self, value):
        if self.sum(self.size) < value:
            return -1
        elif value <= 0:
            return 0

        m = 1
        while m < self.size:
            m *= 2

        k = 0
        k_sum = 0
        while m > 0:
            k0 = k + m
            if k0 < self.size:
                if k_sum + self.array[k0] < value:
                    k_sum += self.array[k0]
                    k += m
            m //= 2
        if k < self.size:
            return k + 1
        else:
            return -1

def main():
    N = int(input())
    S = input()

    s_array = [ord(s) - ord("A") for s in S]
    total_num = [0] * 26
    shift_num = 0
    for s in s_array:
        total_num[s] += 1

    agct_num = 0
    for s in ("A", "G", "C", "T"):
        agct_num += total_num[ord(s) -ord("A")]
    
    bit = BinaryIndexTree(N)
    for i in range(N):
        bit.add(i + 1, 1)

    count = 0
    while agct_num > 0:
        index = bit.least_upper_bound(agct_num)
        target_s = s_array[index - 1]
        target_s += shift_num
        target_s %= 26

        total_num[target_s] -= 1
        n = total_num[target_s]
        bit.add(index, -1)

        shift_num += n
        shift_num %= 26

        new_total_num = [0] * 26
        for i in range(26):
            new_total_num[(i + n) % 26] = total_num[i]
        total_num = new_total_num

        agct_num = 0
        for s in ("A", "G", "C", "T"):
            agct_num += total_num[ord(s) -ord("A")]
        count += 1
    
    print(count)











if __name__ == "__main__":
    main()