Acyclic Graph Edges

Given an undirected graph, your task is to choose a direction for each edge so that the resulting directed graph is acyclic. Input The first input line has two integers n and m: the number of nodes and edges. The nodes are numbered 1,2,\dots,n. After this, there are m lines describing the edges. Each line has two distinct integers a and b: there is an edge between nodes a and b. Output Print