#include<cstdio>
#include<string>
#include<vector>
#include<bitset>

using namespace std;

#ifdef HOME
const string inputFile = "input.txt";
const string outputFile = "output.txt";
#else
const string problemName = "ciclueuler";
const string inputFile = problemName + ".in";
const string outputFile = problemName + ".out";
#endif

const int NMAX = 100000 + 5;

int N, M;
vector<int> V[NMAX];
bitset<NMAX> viz;
vector<int> S, sol;

void dfs(int x) {
    viz[x] = 1;
    for(auto y : V[x])
        if(!viz[y])
            dfs(y);
}

int is_euler() {
    int i;

    dfs(1);

    for(i = 1; i <= N; i++)
        if(!viz[i] || V[i].size() % 2)
            return 0;

    return 1;
}

void erase(int x, int y) {
    for(auto &z : V[x])
        if(z == y) {
            swap(V[x].back(), z);
            V[x].pop_back();
            return;
        }
}

void get_euler() {
    int x, y;

    S.push_back(1);

    while(!S.empty()) {
        x = S.back();

        if(V[x].empty()) {
            S.pop_back();
            sol.push_back(x);
        } else {
            y = V[x][0];

            erase(x, y);
            erase(y, x);

            S.push_back(y);
        }
    }
}

int main() {
    int i, x, y;

    freopen(inputFile.c_str(), "r", stdin);
    freopen(outputFile.c_str(), "w", stdout);

    scanf("%d%d", &N, &M);

    while(M--) {
        scanf("%d%d", &x, &y);
        V[x].push_back(y);
        V[y].push_back(x);
    }

    if(is_euler()) {
        get_euler();
        for(i = 0; i < sol.size() - 1; i++)
            printf("%d ", sol[i]);
    } else
        printf("-1\n");

    return 0;
}