#include <fstream>
#include <vector>
#include <stack>
#include <unordered_set>

using namespace std;

ifstream fin("ciclueuler.in");
ofstream fout("ciclueuler.out");

const int nmax = 100000;
const int mmax = 500000;

struct str {
    int x, y;
};

vector <str> g[nmax+1];
bool un[nmax+1];

void dfs( int x ) {
    un[x] = 1;
    for ( int i = 0; i < int(g[x].size()); ++i ) {
        int xn = g[x][i].x;
        if ( un[xn] == 0 ) {
            dfs(xn);
        }
    }
}

stack <int> s;
bool um[mmax+1];

bool g_empty( int x ) {
    while ( g[x].size() > 0 && um[g[x][g[x].size()-1].y] != 0 ) {
        g[x].pop_back();
    }
    return g[x].empty();
}

int main( ) {
    int n, m;
    fin >> n >> m;
    for ( int i = 1; i <= m; ++ i ) {
        int x, y;
        fin >> x >> y;
        str aux;
        aux.x = y;
        aux.y = i;
        g[x].push_back(aux);
        aux.x = x;
        g[y].push_back(aux);
    }

    int ok = 1;
    dfs(1);
    for ( int i = 1; i <= n; ++ i ) {
        if ( g[i].size()%2 == 1 || un[i] == 0 ) {
            ok = 0;
        }
    }

    if ( ok == 1 ) {
        s.push(1);
        for ( int i = 1; i <= m; ++ i ) {
            int x = s.top();
            while ( g_empty(x) == 0 ) {
                str y = g[x][g[x].size()-1];
                g[x].pop_back();
                um[y.y] = 1;
                x = y.x;
                s.push(x);
            }
            fout << x << " ";
            s.pop();
        }
    } else {
        fout << "-1\n";
    }

    return 0;
}