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