#include <cstdio>
#include <vector>

using namespace std;

const int N = 100000 + 7;
const int M = 5 * N;
int n;
int m;
int Xor[M];
int sol[M];
int top;
vector<int> g[N];
bool used[M];

void dfs(int a) {
        while (!g[a].empty()) {
                int i = g[a].back();
                g[a].pop_back();
                if (used[i] == 0) {
                        used[i] = 1;
                        dfs(Xor[i] ^ a);
                }
        }
        sol[++top] = a;
}

int main() {
        freopen ("ciclueuler.in", "r", stdin);
        freopen ("ciclueuler.out", "w", stdout);

        scanf("%d %d", &n, &m);
        for (int i = 1; i <= m; i++) {
                int x, y;
                scanf("%d %d", &x, &y);
                Xor[i] = x ^ y;
                g[x].push_back(i);
                g[y].push_back(i);
        }
        for (int i = 1; i <= n; i++) {
                if ((int) g[i].size() % 2 == 1) {
                        printf("-1\n");
                        return 0;
                }
        }
        dfs(1);
        for (int i = 1; i <= m; i++) {
                printf("%d ", sol[i]);
        }
        printf("\n");
}