input();r=input()
S = list(map(int, list(r)))
count = 0
for i in range(1, len(S)):
    if S[i-1:i+1] == [0, 0]:
        count += 1
        S[i] = 1
    elif i >= 2 and S[i-2:i+1] == [0, 1, 0]:
        count += 1
        S[i] = 1
print(count)