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