N = int(input())
S = input().strip()

ans = 0
i = 0
while i < N:
    if S[i] == '0':
        count = 0
        while i < N and S[i] == '0':
            count += 1
            i += 1
        if count % 2 == 1:
            ans += count // 2
        else:
            ans += (count - 1)
    else:
        i += 1
print(ans)