n = int(input())
s = list(input())
result = 0

for i in range(n):
    if s[i] == '0' and i + 1 < n and s[i + 1] == '0':
        result += 1
        s[i + 1] = '1'
    elif s[i] == '1' and 0 < i < n - 1 and s[i - 1] == '0' and s[i + 1] == '0':
        result += 1
        s[i + 1] = '1'

print(result)