N=int(input())
S=input()
D={}
D['c']=[0,0,0]
D['o']=[0,0,0]
D['n']=[0,0,0]
for i in range(3*N):
  s=S[i]
  if s not in D:
    D[s]=[0]*3
  D[s][i%3]+=1

a=min(D['c'][0],D['o'][1],D['n'][2])
b=min(D['c'][1],D['o'][2],D['n'][0])
c=min(D['c'][2],D['o'][0],D['n'][1])
d=a+b+c
if N!=d:
  print(d)
else:
  if S=='con'*N:
    print(d)
  else:
    print(d-1)