# 計算量 O(N^3)

n = int(input())
s = input()
co = s.count("1")
ans = 10**15

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

for l in range(n):
  x = list(range(l+n, l+n+co))
  anss = (n-(l+co)) % n
  sp_l = (l+co) % n
  sp_r = (0 if sp_l == 0 else n)
  for ll in range(co+co+co):
    y = a[ll:ll+co]
    flag = 0
    le = 0
    ri = 0
    for i in range(co):
      if y[i] <= x[i]:
        if sp_l <= y[i] % n < sp_r:
          le = max(le, x[i]-y[i]-1)
        else:
          le = max(le, x[i]-y[i])
      else:
        if sp_l <= y[i] % n <= sp_r:
          flag = 1
        if ri == 0:
          ri += 1
        ri += 1
    ri -= flag
    ans = min(ans, anss+max(le, ri)*n)
print(ans)