N = int(input())
S = input()

xs = [int(c) for c in S]
ans = 0
for i in range(N):
    if xs[i] == 0:
        if i > 0 and xs[i-1] == 0:
            xs[i] = 1
            ans += 1
        if i > 1 and xs[i-2] == 0:
            xs[i] = 1
            ans += 1

print(ans)