N = int(input())
S = input()
s = []
for i in range(N):
	s.append(S[i])
ans = 0
for i in range(N-4):
	if s[i+2] == 0:
		if s[i] == 0:
			s[i] == 1
			ans = ans + 1
		if s[i+1] == 0:
			s[i+1] == 1
			ans = ans + 1
		if s[i+3] == 0:
			s[i+3] == 1
			ans = ans + 1
		if s[i+4] == 0:
			s[i+4] == 1
			ans = ans + 1
print(ans)