N = int(input())
S = [int(x) for x in input()]

if N == 1:
  exit(print(0))
elif N == 2:
  exit(print(int(sum(S)==0)))

ans = 0
if sum(S[:3]) == 0:
  S[0] = 1
  ans += 1
for i in range(N-2):
  if S[i]+S[i+1]+S[i+2] < 2:
    ans += 1
    for j in range(i, i+3)[::-1]:
      if S[j]==0:
        S[j] = 1
        break

print(ans)