N = int(input())
s = input()
S = [int(i) for i in s]
if N == 1:
	ans = 0
elif N == 2:
	ans = 1 if S == [0,0] else 0
else:
	ans = 0
	for i in range(N-2):
		if S[i] == 0:
			if S[i+1] == 0:
				S[i+1] = 1
				ans += 1
			if S[i+2] == 0:
				S[i+2] = 1
				ans += 1	
print(ans)