import collections
N = int(input())
S = list(input())
C = [collections.Counter() for _ in range(3)]
for i,c in enumerate(S):
    C[i%3][c]+=1
print(min(C[0]['c'],C[1]['o'],C[2]['n'])+min(N-1,min(C[0]['o'],C[1]['n'],C[2]['c']))+min(N-1,min(C[0]['n'],C[1]['c'],C[2]['o'])))