def main():
    import sys
    input = sys.stdin.read
    data = input().split()
    N = int(data[0])
    S = data[1]
    len_S = 3 * N

    mod0 = []
    mod1 = []
    mod2 = []
    for i in range(len_S):
        c = S[i]
        if i % 3 == 0:
            mod0.append(c)
        elif i % 3 == 1:
            mod1.append(c)
        else:
            mod2.append(c)

    from collections import defaultdict

    def count_chars(arr):
        cnt = defaultdict(int)
        for c in arr:
            cnt[c] += 1
        return cnt

    cnt0 = count_chars(mod0)
    cnt1 = count_chars(mod1)
    cnt2 = count_chars(mod2)

    c0 = cnt0.get('c', 0)
    o1 = cnt1.get('o', 0)
    n2 = cnt2.get('n', 0)
    case1 = min(c0, o1, n2)

    c1 = cnt1.get('c', 0)
    o2 = cnt2.get('o', 0)
    n0 = cnt0.get('n', 0)
    case2 = min(c1, o2, n0)

    c2 = cnt2.get('c', 0)
    o0 = cnt0.get('o', 0)
    n1 = cnt1.get('n', 0)
    case3 = min(c2, o0, n1)

    total = case1 + case2 + case3
    print(total)

if __name__ == "__main__":
    main()