def hyx(s: str, index: int):#實現(xiàn)數(shù)字互換
    x = list(s)
    x[index], x[index + 1] = x[index + 1], x[index]
    s = "".join(x)
    return s


def maya(n, x: str):#求解最少次數(shù)
    if "2012" in x:
        return 0
    if x.count("2") < 2 or x.count("1") < 1 or x.count("0") < 1:
        return -1
    ct = 0
    ans = []
    ans.append(x)
    zc = []
    while True:
        ans += zc
        for s in ans:#遍歷每一層
            for i in range(len(s) - 1):#每一層內(nèi)遍歷檢查
                if "2012" in s:
                    return ct
                zc.append(hyx(s, i))
        ct += 1


while True:
    try:
        n = int(input())
        s = input()
        print(maya(n, s))
    except:
        break