#include <cstdio>
#include <vector>
#include <list>
#include <stack>
#include <algorithm>

using namespace std;

list<int>ls[100005];
vector<int>sol;
bool viz[100005],ok;
int n, m,i,j,x,y;
stack<int>stiva;

int main() {
    freopen("ciclueuler.in","r",stdin);
    freopen("ciclueuler.out","w",stdout);
    scanf("%d %d\n", &n, &m);
    while (m--) {
        scanf("%d %d\n", &x,&y);
        ls[x].push_back(y);
        ls[y].push_back(x);
    }
    for (i = 1; i<= n; i++)
        if (ls[i].size()%2==1) {
            printf("-1");
            return 0;
        }
    stiva.push(1);
    while (stiva.empty()==0) {
        x = stiva.top();
        while (ls[x].size() > 0) {
            y = ls[x].front();
            stiva.push(y);
            ls[x].erase(ls[x].begin());
            ls[y].erase(find(ls[y].begin(), ls[y].end(), x));
            x = y;
        }
        sol.push_back(stiva.top());
        stiva.pop();
    }
    for (auto &it:sol)
        printf("%d ", it);

    return 0;
}