#include <iostream>
#include <cstdint>
#include <algorithm>

static inline constexpr uint_fast32_t solve(const uint_fast32_t N, const std::string& S) noexcept
{
	uint_fast32_t len_neg = 0, len_zero = 0, len_pos = 0;
	for (uint_fast32_t i = 0; i != N; ++i)
		switch(S[i])
		{
		case '-':
			++len_neg;
			break;

		case '0':
			len_zero = len_neg + 1;
			break;

		case '1':
			len_pos = std::max({ len_neg, len_zero, len_pos }) + 1;
			break;
		}

	return std::max({ len_neg, len_zero, len_pos });
}

int main()
{
	std::cin.tie(nullptr);
	std::ios::sync_with_stdio(false);
	
	uint_fast32_t N;
	std::string S;
	std::cin >> N;
	S.reserve(N), std::cin >> S;

	std::cout << solve(N, S) << '\n';
	return 0;
}