I,R=input,range
N=int(I())*3
S=I()
a=0
s="con"
for d in R(3):
	c=[0]*3
	for i in R(N):c[i%3]+=S[i]==s[(i+d)%3]
	a+=min(min(c),(N-a*3-d)//3)
print(a)