# O(N log^2 N)

from bisect import bisect_left,bisect_right
def solve4(n,s):
  ans=10**10

  zero=s.count("0")
  one=n-zero
  if zero==0 or zero==n:
    return 0

  se=set()
  if s[0]=="1":
    se.add(0)
    for i in range(n-1,-1,-1):
      if s[i]=="1":
        se.add(i)
      else:break

  po=[]
  for i in range(n):
    if s[i]=="1":po+=[i,i+n,i+n+n,i+n+n+n]
  po.sort()

  def f(l,ll):
    sp_l=(l+one)%n
    sp_r=n
    if sp_l==0:sp_l=n
    ansl=0
    ansr=0
    flag=True
    flagg=False
    if po[ll]<=l+n:
      if sp_l<=((po[ll]-1)%n+1)<=sp_r and (po[ll]%n not in se):
        ansl=l+n-po[ll]-1
      else:
        ansl=l+n-po[ll]
    if l+n+one-1<po[ll+one-1]:
      flag=True
      flagg=False
      ng=-1
      ok=one
      while ng+1!=ok:
        mid=(ng+ok)//2
        if l+n+mid<po[ll+mid]:ok=mid
        else:ng=mid
      x=l+n+ok
      if x%n:x+=n-(x%n)
      if x<=l+n+one-1:
        if l+n+ok<=po[ll+ok]<=x:
          flagg=True
        x+=n
      if l+n+ok<=po[ll+ok]<=x:
        flag=False
      ansr=one-ok
      if ansr:ansr+=flag
      ansr-=flagg
    return max(ansl,ansr)

  for l in range(n):
    anss=(-l-one)%n
    sp_l=(l+one)%n
    sp_r=n
    if sp_l==0:sp_l=n
    ng=-1
    ok=n
    while ng+1!=ok:
      mid=(ng+ok)//2
      x=l+n-mid-1
      if not(sp_l<=((x-1)%n+1)<=sp_r and (x%n not in se)):x+=1
      ll=bisect_left(po,x)
      if f(l,ll)<=mid:ok=mid
      else:ng=mid
    ans=min(ans,anss+ok*n)
  return ans

def solve3(n,s):
  ans=10**10

  zero=s.count("0")
  one=n-zero
  if zero==0 or zero==n:
    return 0

  se=set()
  if s[0]=="1":
    se.add(0)
    for i in range(n-1,-1,-1):
      if s[i]=="1":
        se.add(i)
      else:break

  po=[]
  for i in range(n):
    if s[i]=="1":po+=[i,i+n,i+n+n,i+n+n+n]
  po.sort()

  for l in range(n):
    a=list(range(l+n,l+one+n))
    sp_l=(l+one)%n
    sp_r=n
    if sp_l==0:sp_l=n

    for ll in range(one*3):
      ansl=0
      ansr=0
      flag=True
      flagg=False
      if po[ll]<=a[0]:
        if sp_l<=((po[ll]-1)%n+1)<=sp_r and (po[ll]%n not in se):
          ansl=a[0]-po[ll]-1
        else:
          ansl=a[0]-po[ll]
      if a[one-1]<po[ll+one-1]:
        flag=True
        flagg=False
        ng=-1
        ok=one
        while ng+1!=ok:
          mid=(ng+ok)//2
          if a[mid]<po[ll+mid]:ok=mid
          else:ng=mid
        x=a[ok]
        if x%n:x+=n-(x%n)
        if x<=a[one-1]:
          if a[ok]<=po[ll+ok]<=x:
            flagg=True
          x+=n
        if a[ok]<=po[ll+ok]<=x:
          flag=False
        ansr=one-ok
        if ansr:ansr+=flag
        ansr-=flagg
      print(l,ll,max(ansl,ansr)*n+(-l-one)%n)
      ans=min(ans,max(ansl,ansr)*n+(-l-one)%n)
    
  return ans

def solve2(n,s):
  ans=10**10
  zero=s.count("0")
  one=n-zero
  if zero==0 or zero==n:
    return 0
  se=set()
  if s[0]=="1":
    se.add(0)
    for i in range(n-1,-1,-1):
      if s[i]=="1":
        se.add(i)
      else:break
  for l in range(n):
    a=list(range(l+n,l+one+n))
    sp_l=(l+one)%n
    sp_r=n
    if sp_l==0:sp_l=n
    for ll in range(n*3):
      b=[]
      for i in range(ll,ll+n):
        if s[i%n]=="1":b.append(i)
      ansl=0
      ansr=0
      flag=True
      flagg=False
      if b[0]<=a[0]:
        if sp_l<=((b[0]-1)%n+1)<=sp_r and (b[0]%n not in se):
          ansl=a[0]-b[0]-1
        else:
          ansl=a[0]-b[0]
      for i in range(one):
        if b[i]>a[i]:
          ansr+=1
          x=a[i]
          if x%n:x+=n-(x%n)
          if x<=a[-1]:
            if a[i]<=b[i]<=x:
              flagg=True
            x+=n
          if a[i]<=b[i]<=x:
            flag=False
      if ansr:ansr+=flag
      ansr-=flagg
      ans=min(ans,max(ansl,ansr)*n+(-l-one)%n)
  return ans

from collections import defaultdict, deque
def solve1(n,s):
  cost = defaultdict(int)
  cost[s] = 0
  goal = "".join(sorted(list(s)))
  que = deque([s])
  while que:
    t = que.popleft()
    if t == goal:
      return cost[t]
    t1 = t[-1] + t[:-1]
    t2 = t[0] + t[-1] + t[1:-1]
    if t1 not in cost:
      cost[t1] = cost[t] + 1
      que.append(t1)
    if t2 not in cost:
      cost[t2] = cost[t] + 1
      que.append(t2)

from random import randint
t="01"
while 0:
  n=randint(50,100)
  s="".join([t[randint(0,1)]for i in range(n)])
  ans3=solve3(n,s)
  ans4=solve4(n,s)
  if ans4!=ans3:
    print("ERROR!!")
    print(n)
    print(s)
    print("ans3 =",ans3)
    print("ans4 =",ans4)
    exit()
  print("ok")

n=int(input())
s=input()
#print(solve3(n,s))
print(solve4(n,s))