N = int(input())
S = bytearray(input().encode())
cnt = 0

for i in range(1, N):
    if S[i] == 49:
        continue
    if S[i - 1] == 48 or (i >= 2 and S[i - 2] == 48):
        S[i] = 49
        cnt += 1

print(cnt)