#include<fstream>
#include <iostream>
#include <vector>
#include <list>
using namespace std;
const int MAX_N =10000;
const int MAX_M =10000;


int vertex[MAX_M][MAX_M];
int visited[MAX_M];
int circuit[MAX_M];
int edges[MAX_M];
int circuitpos;

void dfs(int s){
    bool used = true;
    while(used){
        used=false;
        for (int i = 0; i < MAX_M; i++) {
            if (vertex[s][i] > 0) {
               used = true;
               vertex[s][i]--;
               vertex[i][s]--;
               dfs(i);
            }
        }
    }
    circuit[circuitpos++] = s;
}


int main() {
   ifstream fin("input.txt");
   ofstream fout("output.txt");
   int n,m; fin >> n>>m;
   int x, y,u,v;
   fin >> u>>v;
   int start = u ;
   for (int i = 0; i < m; i++) {
      fin >> x >> y;
      vertex[x][y]++;
      vertex[y][x]++;
      edges[x]++;
      edges[y]++;
      start = min(start, min(x, y));
   }
   for (int i = MAX_M; i >= 0; i--) if (edges[i] % 2 != 0) { start = i; }
   dfs(start);
   for (int i = circuitpos-1; i >= 1; i--) fout << circuit[i] << circuit[i-1]<< "\n";
   return 0;
}