n = int(input())
s = [v for v in input()]

ans = 0
for i in range(n):
    if s[i] == "1":
        continue
    
    if i - 1 >= 0:
        if s[i - 1] == "0":
            s[i] = "1"
            ans += 1
            continue
        
    if i - 2 >= 0:
        if s[i - 2] == "0" and s[i - 1] == "1":
            s[i] = "1"
            ans += 1
            continue
        
print(ans)