n = int(input())
s = list(input())
ans = 0
prev = "1"
prev2 = "1"
for c in s:
    if c == "0":
        if prev == "1" and prev2 == "1":
            pass
        else:
            c = "1"
            ans += 1
    prev2 = prev
    prev = c
print(ans)