from collections import defaultdict

n = int(input())
S = list(input())

C = [defaultdict(int) for _ in range(3)]
for i in range(3 * n):
    C[i % 3][S[i]] += 1
ans = 0
for i in range(3):
    ans += min(C[i % 3]['c'], C[(i + 1) % 3]['o'], C[(i + 2) % 3]['n'])
print(ans)