import heapq
n = int(input())
s = list(input())
ans = 0
for i in range(n):
    if s[i] == '0':
        if i > 0 and s[i-1] == "0":
            ans += 1
            s[i] = '1'
        if i > 1 and s[i - 2] == '0':
            ans += 1
            s[i] = '1'
print(ans)