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 and i + 1 < n:
        if s[i - 1] == "1" and s[i + 1] == "1":
            continue
        
        s[i] = "1"
        ans += 1
    elif i - 1 >= 0:
        if s[i - 1] == "1":
            continue
        
        s[i] = "1"
        ans += 1
    else:
        if s[i + 1] == "1":
            continue
        
        s[i] = "1"
        ans += 1
        
print(ans)