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

ans = 0
for i in range(n):
    if i >= 1 and s[i] == "0" and s[i-1] == "0":
        s[i] = "1"
        ans += 1
    if i >= 2 and s[i] == "0" and s[i-1] == "1" and s[i-2] == "0":
        s[i] = "1"
        ans += 1

print(ans)