n = int(input())
s =list(input().rstrip())
ans = 0
for i in range(n):
    if i-2 >= 0 and s[i-2] == '0' and s[i-1] == '1' and s[i] == '0':
        s[i] = '1'
        ans += 1
    if i-1 >= 0 and s[i-1] == s[i] == '0':
        s[i] = '1'
        ans += 1
print(ans)