#include<fstream>
using namespace std;
ifstream fin ("secv2.in");
ofstream fout("secv2.out");
int main()
{
	fin >> n >> k;
	while (fin >> raspuns1)
	{
		if (n > k)
		{	fout << 0;
			break;
		}
		if (raspuns1 == 0)
			fin >> raspuns2;
		else
		{
			fout << (k - n) / 2;
			break;
		}
		if (raspuns2 == 1)
			k = (k - n) / 2;
		else
			n = (k - n) / 2;
	}
}