n = int(input())
s = input().strip()
res = 0
i = 0
while i < n:
    if s[i] == '0':
        j = i
        while j < n and s[j] == '0':
            j += 1
        length = j - i
        res += (length + 1) // 2
        i = j
    else:
        i += 1
print(res)