n = int(input())
s = ['1', '1'] + list(input()) + ['1', '1']
n = len(s)
ans = 0
for i in range(1, n-1):
	if s[i-1]=='0' and s[i]=='0':
		s[i] = '1'
		ans += 1
	elif i+1<n and s[i-1]=='0' and s[i]=='1' and s[i+1]=='0':
		s[i+1] = '1'
		ans += 1

print(ans)