const int maxn = 100010;
int n, m;
vector <int> G[maxn*2];
bool mark[maxn*2];
int S[maxn*2], c;
int a[maxn], b[maxn], sum;
bool dfs(int x)
{
	if(mark[x^1])
		return false;
	if(mark[x])
		return true;
	mark[x] = true;
	S[c++] = x;
	for(int i = 0; i < G[x].size(); i++)
		if(!dfs(G[x][i]))
			return false;
	return true;
}

void init()
{
	for(int i = 0; i < n*2; i++)
		G[i].clear();
	memset(mark, 0, sizeof(mark));
}

void AddEdge(int u, int v, int x, int y)
{
	u = u * 2 + x;
	v = v * 2 + y;
	G[u].push_back(v^1);
	G[v].push_back(u^1);
}
bool solve()
{
	for(int i = 0; i < n*2; i += 2)
	{
		if(!mark[i] && !mark[i+1])
		{
			c = 0;
			if(!dfs(i))
			{
				while(c > 0)
					mark[S[--c]] = false;
				if(!dfs(i+1))
					return false;
			}
		}
	}
	return true;
}