import sys, random
input = lambda : sys.stdin.readline().rstrip()


write = lambda x: sys.stdout.write(x+"\n"); writef = lambda x: print("{:.12f}".format(x))
debug = lambda x: sys.stderr.write(x+"\n")
YES="Yes"; NO="No"; pans = lambda v: print(YES if v else NO); INF=10**18
LI = lambda : list(map(int, input().split())); II=lambda : int(input()); SI=lambda : [ord(c)-ord("a") for c in input()]
def debug(_l_):
    for s in _l_.split():
        print(f"{s}={eval(s)}", end=" ")
    print()
def dlist(*l, fill=0):
    if len(l)==1:
        return [fill]*l[0]
    ll = l[1:]
    return [dlist(*ll, fill=fill) for _ in range(l[0])]

n = int(input())
s = SI()
l = [[],[],[]]
for i in range(3*n):
    l[i%3].append(s[i])
from collections import Counter
C = ord("c")-ord("a")
O = ord("o")-ord("a")
N = ord("n")-ord("a")
cs = [Counter(item) for item in l]
ans = 0
val = min(cs[0][C], cs[1][O], cs[2][N])
val2 = min(cs[1][C], cs[2][O], cs[0][N])
if val2==n:
    val2 = n-1
val3 = min(cs[2][C], cs[0][O], cs[1][N])
if val3==n:
    val3 = n-1
ans = val + val2 + val3
if ans==n and val!=n:
    ans = n-1
print(ans)