#include <fstream>
#include <vector>
#include <bitset>
#include <queue>
#include <algorithm>
#include <utility>
#include <string.h>
#include <stack>

using namespace std;

ifstream cin("euler.in");
ofstream cout("euler.out");

const int MAXN = 100005;
const int oo = (1<<31)-1;

typedef vector<int> Graph[MAXN];
typedef vector<int> :: iterator It;

Graph G;
stack<int> Stack;
int N, M;

const inline void CheckEulerProperty(){
    for(int i = 1 ; i <= N ; ++ i){
        if(!G[i].size() || G[i].size() & 1){
            cout << "-1\n";
            exit(EXIT_SUCCESS);
        }
    }
}

inline void DFs(){
    Stack.push(1);
    while(!Stack.empty()){
        int x = Stack.top();
        if(G[x].size()){
            int y = G[x].back();
            G[x].pop_back();
            G[y].erase(find(G[y].begin(), G[y].end(), x));
            Stack.push(y);
        }
        else{
            Stack.pop();
            if(!Stack.empty())
                cout << x << " ";
        }
    }
}

int main()
{
    cin >> N >> M;
    for(int i = 1 ; i <= M ; ++ i){
        int X, Y;
        cin >> X >> Y;
        G[X].push_back(Y);
        G[Y].push_back(X);
    }
    CheckEulerProperty();
    DFs();
    cin.close();
    cout.close();
    return 0;
}