from collections import deque
N = int(input())
S = list(input())

cnt = 0

hoge = 3
q = deque(['1','1','1'])

for c in S:
    #print(q,hoge)
    a = q.popleft()
    if a == '1':
        hoge -= 1
    q.append(c)
    if c == '1':
        hoge += 1
    
    if hoge < 2:
        q[2] = '1'
        hoge += 1
        cnt += 1
print(cnt)