#include <cstdio>
#include <vector>
#include <stack>
#include <algorithm>
using namespace std;

const int nmx = 100005;

int n, m, grad[nmx];
vector <int> g[nmx];

void euler(){
    stack <int> s;
    s.push(1);
    while(not s.empty()){
        int nod = s.top();
        if(g[nod].size()){
            int fiu = g[nod].back();
            s.push(fiu);
            g[nod].pop_back();
            g[fiu].erase(find(g[fiu].begin(),g[fiu].end(),nod));
        }
        else{
            printf("%d ", nod);
            s.pop();
        }
    }
}

int main() {
    freopen("ciclueuler.in", "r", stdin);
    freopen("ciclueuler.out", "w", stdout);
    scanf("%d %d", &n, &m);
    for(; m; --m) {
        int n1, n2;
        scanf("%d %d", &n1, &n2);
        g[n1].push_back(n2);
        g[n2].push_back(n1);
        ++ grad[n1];
        ++ grad[n2];
    }
    for(int i = 1; i <= n; ++i)
        if(grad[i] % 2) {
            printf("-1\n");
            return 0;
        }
    euler();
    return 0;
}