import java.util.*;

public class topologicalSort{
    static int N;
    static int[][] graph;
    static boolean[] visited;
    static Stack<Integer> stack = new Stack<>();

    static void dfs(int v){
        visited[v] = true;
        for(int i =0;i<N;i++){
            if(!visited[i] && graph[v][i]==1){
                dfs(i);
            }
        }
        stack.push(v);
    }

    static void topoSort(){
        for(int i=0;i<N;i++){
            if(!visited[i]){
                dfs(i);
        }
    }

    System.out.println("\nValid execution order");
    while(!stack.isEmpty()){
        System.out.print((char)('A'+ stack.pop())+"->");
    }
    }
    public static void main(String[] args){
        Scanner sc = new Scanner(System.in);
        System.out.print("\nEnter number of tasks: ");
        N = sc.nextInt();
        graph = new int[N][N];
        visited = new boolean[N];

        System.out.print("ENter number of dependencies: ");
        int edges = sc.nextInt();

        System.out.println("Enter dependencies (u v means u -> v):");
        for(int i = 0;i<edges;i++){
            char u = sc.next().charAt(0);
            char v = sc.next().charAt(0);

            graph[u-'A'][v-'A'] = 1;
        }
        topoSort();
        sc.close();
    
    }
    
}