from collections import defaultdict


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

    A=[defaultdict(int), defaultdict(int), defaultdict(int)]

    for i in range(3*N):
        A[i%3][S[i]]+=1

    p,q,r="con"
    ans=0

    for _ in range(3):
        ans+=min(A[0][p],A[1][q],A[2][r])
        p,q,r=q,r,p
    return ans

print(solve())