def main():
    from sys import stdin, setrecursionlimit
    # setrecursionlimit(1000000)
    input = stdin.readline
    def iinput(): return int(input())
    def sinput(): return input().rstrip()
    def i0input(): return int(input()) - 1
    def linput(): return list(input().split())
    def liinput(): return list(map(int, input().split()))
    def miinput(): return map(int, input().split())
    def li0input(): return list(map(lambda x: int(x) - 1, input().split()))
    def mi0input(): return map(lambda x: int(x) - 1, input().split())
    INF = 1000000000000000000
    MOD = 1000000007

    N = iinput()
    S = sinput()

    ans = [[0] * 3 for _ in [0] * 3]
    con = 'con'
    for i in range(N * 3):
        c = S[i]
        try:
            j = con.index(c)
        except ValueError:
            continue
        ans[(i-j)%3][j%3] += 1
    # print(ans)
    print(min(ans[0]) + min(ans[1]) + min(ans[2]))

main()