N = int(input())
S = list(input())
ans = 0
for i in range(N - 1):
    if S[i:i + 2] == ["0", "0"]:
        S[i + 1] = "1"
        ans += 1
    if i < N - 2 and S[i:i + 3] == ["0", "1", "0"]:
        S[i + 2] = "1"
        ans += 1
print(ans)