def main():
	n = int(input())
	if n==1:
		print(0)
		return
	ans = 0
	s = list(input())
	for i in range(n-2):
		if s[i+2]=="0" and not(s[i]==s[i+1]=="1"):
			s[i+2] = "1"
			ans += 1
	print(ans)
	
	
if __name__ == "__main__":
	main()