#include <bits/stdc++.h>

static inline constexpr uint_fast64_t solve(const uint_fast32_t N, const uint_fast64_t A, const std::string& _S) noexcept
{
	uint_fast32_t loss = 0, i;
	uint_fast64_t AC_count = 0;
	for (i = 0; i != N; ++i)
	{
		if (AC_count == A)
			return i;
		else if (_S[i] == '0')
			++loss;
		else if (loss != 0)
			--loss, ++AC_count;
	}
	if (AC_count == A)
		return i;

	uint_fast32_t AC_count_per_cycle = 0;
	for (i = 0; i != N; ++i)
	{
		if (_S[i] == '0')
			++loss;
		else if (loss != 0)
			--loss, ++AC_count_per_cycle;
	}

	const uint_fast32_t count_cycle = (A - AC_count + AC_count_per_cycle - 1) / AC_count_per_cycle - 1;
	AC_count += static_cast<uint_fast64_t>(AC_count_per_cycle) * count_cycle;
	for (i = 0; AC_count != A; ++i)
	{
		if (_S[i] == '0')
			++loss;
		else if (loss != 0)
			--loss, ++AC_count;
	}

	return N * (count_cycle + 1) + i;
}

int main()
{
	std::cin.tie(nullptr);
	std::ios::sync_with_stdio(false);

	uint_fast32_t N;
	uint_fast64_t A;
	std::string _S;
	std::cin >> N >> A;
	_S.reserve(N), std::cin >> _S;

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