n=int(input())
s=[*input()]
t=s[:]
ans=0
for i in range(n):
  if '0'in s[i-2:i] and s[i]=='0':
    s[i]='2'
    ans+=1
ans1=0
s2=t[:]
for i in range(n)[::-1]:
  if '0'in s2[i+1:i+3] and s2[i]=='0':
    s2[i]='2'
    ans1+=1
print(min(ans,ans1))
# print(''.join(s))
# print(''.join(s2))