Safe Routes

Alice is the queen of ChefLand. She has initiated a road reform recently. The reform will last for M days. Initially, there are N towns and no roads in ChefLand. Every day one bidirectional road will be built. On the i-th day, the road connecting the towns Ai and Bi will be built. Nevertheless, Alice worries that if there is a road that will occur in every route from the town A to the town B f