The directed unweighted graph is given. Find the lexicographically smallest topological ordering of its vertices.
The first line contains the number of vertices n (1≤n≤105) and the number of edges m (1≤m≤105) in a graph. Each of the next m lines describes the edge of the graph — two numbers, the initial and final vertex.
Print the lexicographically smallest topological ordering of graph's vertices. If its impossible to sort graph topologically, print −1.