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

s = list(s)

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)