#include <iostream>
#include <fstream>
#include <vector>
#include <stack>
#define FIN "ciclueuler.in"
#define FOUT "ciclueuler.out"
#define NMAX 100005
#define MMAX 700005
 
using namespace std;
 
vector<int> G[ NMAX ];
stack<int> STACK;
 
int degree[ NMAX ],
 
    sol[ MMAX ],
 
    num_nodes, 
 
    num_edges,
 
    i,
    x,
    y,
    a,
    b;
  
int main() {
 
    freopen(FIN, "r", stdin);
 
    freopen(FOUT, "w", stdout);
 
    scanf("%d %d", &num_nodes, &num_edges);
 
    for(i = 1; i <= num_edges; i++) {
 
          scanf("%d %d", &x, &y);
 
          G[ x ].push_back( y );  
          G[ y ].push_back( x );
  
          degree[ x ]++;
          degree[ y ]++;
    }     
 
    fclose( stdin ); 
 
    for(i = 1; i <= num_nodes; i++) {
 
        if(degree[ i ] & 1) {
 
           printf("-1");
 
           return 0; 
        }
    }
 
    STACK.push( 1 );
 
    while(!STACK.empty()) {
 
           a = STACK.top();
 
           if(!degree[ a ]) {
 
               sol[++sol[0]] = a;
               STACK.pop();
               continue;  
           }
 
           b = G[ a ].back();
 
           G[ a ].pop_back();           
 
           degree[ a ]--;
 
           degree[ b ]--;
 
           STACK.push( b ); 
 
           for(vector<int>::iterator it = G[ b ].begin(); it != G[ b ].end(); ++it) {
 
               if(*it == a) {
 
                   G[ b ].erase( it );
                   break;
               }   
           } 
    }
 
    for(i = 1; i <= num_edges; i++) printf("%d ", sol[ i ]); 
 
    fclose( stdout );
 
    return(0);
};