def main():
    try:
        import pypyjit
        pypyjit.set_param('max_unroll_recursion=-1')
    except:
        pass
    try:
        import sys
        sys.setrecursionlimit(10**7)
    except:
        pass
    from math import sqrt,sin,cos,tan,ceil,radians,floor,gcd,exp,log,log10,log2,factorial,fsum
    from heapq import heapify, heappop, heappush
    from bisect import bisect_left, bisect_right
    from copy import deepcopy
    import copy
    import random
    from collections import deque,Counter,defaultdict
    from itertools import permutations,combinations
    from decimal import Decimal,ROUND_HALF_UP
    #tmp = Decimal(mid).quantize(Decimal('0'), rounding=ROUND_HALF_UP)
    from functools import lru_cache, reduce
    #@lru_cache(maxsize=None)
    from operator import add,sub,mul,xor,and_,or_,itemgetter
    INF = 10**18
    mod1 = 10**9+7
    mod2 = 998244353
    
    #DecimalならPython
    
    
    '''
    これもスワップか
    3で割った余りみたいなのが大事そう
    回数の最小値はいらないから
    %3 = 0
    %3 = 1
    %3 = 2
    でc,o,nの数数えて
    それの最小のやつ
    '''
    
    N = int(input())
    S = list(input())
    
    c0 = 0
    o0 = 0
    n0 = 0
    for i in range(0,3*N,3):
        if S[i] == 'c':
            c0 += 1
        elif S[i] == 'o':
            o0 += 1
        elif S[i] == 'n':
            n0 += 1
    
    c1 = 0
    o1 = 0
    n1 = 0
    for i in range(1,3*N,3):
        if S[i] == 'c':
            c1 += 1
        elif S[i] == 'o':
            o1 += 1
        elif S[i] == 'n':
            n1 += 1
    
    c2 = 0
    o2 = 0
    n2 = 0
    for i in range(2,3*N,3):
        if S[i] == 'c':
            c2 += 1
        elif S[i] == 'o':
            o2 += 1
        elif S[i] == 'n':
            n2 += 1
    
    print(min(c0,o1,n2)+min(o0,n1,c2)+min(n0,c1,o2))
    
    
    
    
    
    
    
    
    
    
    
    
    
    
    
    
    
    
    
    
    
    
    
    
    
    
    
    
    
    
if __name__ == '__main__':
    main()