n=int(input())
s=[*input()]
t=s[:]
for i in range(1,n):
  if i==1:
    if s[:2]==[*'00']:
      s[i]='2'
  elif '0'in s[i-2:i] and s[i]=='0':
    s[i]='2'
s2=t[:]
for i in range(n)[::-1]:
  if '0'in s2[i+1:i+3] and s2[i]=='0':
    s2[i]='2'
print(min(s.count('2'),s2.count('2')))
# print(''.join(s))
# print(''.join(s2))