#int(input())
#map(int, input().split())
#list(map(int, input().split()))

N = int(input())
S = input()
m = 3 * N

a = ("c", "o", "n")
c = [[0] * 3 for i in range(3)]

for i in range(m):
    if S[i] in a:
        t = a.index(S[i])
        c[i%3][t] += 1

ans = 0
for i in range(3):
    b = 1000000
    for j in range(3):
        b = min(c[(i+j)%3][j], b)
    ans += b

print(ans)