def min_operations_to_good_string(S):
    N = len(S)
    ones = S.count('1')
    zero_blocks = 0
    i = 0

    while i < N:
        if S[i] == '0':
            start = i
            while i < N and S[i] == '0':
                i += 1
            length = i - start
            if length >= 2:
                zero_blocks += 1
        else:
            i += 1

    ops = 0
    while zero_blocks >= ones:
        ops += 1
        zero_blocks -= 1
        ones += 1
    return ops

if __name__ == "__main__":
    N = int(input())
    S = input().strip()
    print(min_operations_to_good_string(S))