from functools import lru_cache

def solve(N, S):
    if list(S) == sorted(S):
        return 0

    S2 = S * 2
    
    # get #0 in S[l:r] by zero_cnt[r] - zero_cnt[l]
    zero_cnt = [0]
    one_cnt = [0]
    for c in S2:
        zero_cnt.append(zero_cnt[-1] + int(c == '0'))
        one_cnt.append(one_cnt[-1] + int(c == '1'))

    @lru_cache(10)
    def calc(l, t, r):
        left0 = zero_cnt[t + 1] - zero_cnt[l]
        right1 = one_cnt[r + 1] - one_cnt[t + 1]
        end = t + right1
        rem = (N - 1 - end) % N
        assert l <= t <= end <= r
        if end < N:
            if right1:
                rskip = int(bool(one_cnt[N + 1] - one_cnt[t + 1]))
                right1 = right1 + 1 - rskip
            loop = max(left0, right1)
        elif t < N:
            rskip = int(bool(one_cnt[N + 1] - one_cnt[t + 1]))
            loop = max(left0 - 1, right1 - rskip)
        else:
            lskip = int(bool(zero_cnt[N + 1] - zero_cnt[l + 1]))
            loop = max(left0 - lskip, right1)
        loop = max(0, loop)
        return loop * N + rem

    ones = []
    for i, c in enumerate(S2):
        if c == '1':
            ones.append(i)

    answer = 10 ** 18
    
    # debug = []
    t = -1
    for i in range(one_cnt[N]):
        l = ones[i]
        r = ones[i + one_cnt[N] - 1]
        # debug.append([-1] * l + [calc(l, t, r) for t in range(l, r + 1)])
        t = max(l, t)
        while True:
            c = calc(l, t, r)
            # print(l, t, r, c)
            nt = t + 1
            while nt <= r and c == calc(l, nt, r):
                nt += 1
            if nt == r + 1 or c < calc(l, nt, r):
                break
            t = nt
        answer = min(answer, c)        
    
    # print(*debug, sep='\n')

    return answer


def slow(N, S):
    parent = dict()
    sorted_S = sorted(S)
    q = [(0, list(S))]
    while True:
        nq = []
        for t, Sp in q:
            # print(Sp, sorted_S)
            if Sp == sorted_S:
                tr = []
                Sp_str = ''.join(Sp)
                while Sp_str != S:
                    tr.append(Sp_str)
                    Sp_str = parent[Sp_str]
                tr.append(S)
                print(tr[::-1])
                for i in range(len(tr)):
                    k = i % N
                    print(tr[-i-1][k:] + tr[-i-1][:k])
                return t
            newSp = [Sp[-1]] + Sp[:-1]
            nq.append((t + 1, newSp))
            if ''.join(newSp) not in parent:
                parent[''.join(newSp)] = ''.join(Sp)
            newSp = [Sp[0]] + [Sp[-1]] + Sp[1:-1]
            nq.append((t + 1, newSp))
            if ''.join(newSp) not in parent:
                parent[''.join(newSp)] = ''.join(Sp)
        q = nq
    

def main():
    N = int(input())
    S = input()
    print(solve(N, S))
    # print(slow(N, S))

def test(t):
    import random
    for r in range(t):
        S = bin(r)[2:]
        N = len(S)
        # print(N, S)
        ac = slow(N, S)
        wa = solve(N, S)
        # print(ac, wa)
        assert ac == wa
        S = S.replace('1', '2').replace('0', '1').replace('2', '0')
        # print(N, S)
        ac = slow(N, S)
        wa = solve(N, S)
        # print(ac, wa)
        assert ac == wa

main()
# test(1000)