#include<bits/stdc++.h>
#define buff_size (1<<13)
using namespace std;
char buff[buff_size];
int pos=0;
char outBuff[buff_size];
int outPtr;
FILE*f=freopen("ciclueuler.in","r",stdin);
FILE*g=freopen("ciclueuler.out","w",stdout);

int edge_x[500001];
int edge_y[500001];
int viz[500001]= {0};
int ST[500001],k=0;
int n,m,x,y,ok=1;
vector <int> G[100001];

inline void read(int &nr)
{
    while(!isdigit(buff[pos])) if(++pos == buff_size) fread(buff,  1,buff_size, stdin), pos = 0;
    nr = 0;
    while(isdigit(buff[pos]))
    {
        nr = (nr<<1)+(nr<<3)+ buff[pos] - 48;
        if(++pos == buff_size) fread(buff, 1, buff_size, stdin), pos = 0;
    }
}

inline void putChar(const char &C)
{
    outBuff[outPtr++] = C;
    if (outPtr == buff_size) {
        fwrite(outBuff, 1, buff_size, stdout);
        outPtr = 0;
    }
}

inline  void write(int X)
{
    static char digs[10];
    int n = 0, q;
    do {
        q = X / 10;
        digs[n++] = X - (q << 1) - (q << 3) + 48;

        X = q;
    } while (X);
    while (n--) {
        putChar(digs[n]);
    }

}

inline void read_data()
{
    read(n);read(m);
    for(int i=1; i<=m; i++)
    {
        read(x);read(y);
        edge_x[i]=x;
        edge_y[i]=y;
        G[x].push_back(i);
        G[y].push_back(i);
    }
}

inline void euler()
{
    ST[++k]=1;
    while(k)
    {
        int current_node=ST[k];
        if(G[current_node].size())
        {
            int next_node=G[current_node].back();
            G[current_node].pop_back();
            if(viz[next_node]==0)
            {
                viz[next_node]=1;
                if(edge_x[next_node]==current_node) ST[++k]=edge_y[next_node];
                else ST[++k]=edge_x[next_node];
            }
        }
        else k--,write(current_node),putChar(' ');
    }
}

inline void solve()
{
    for(int i=1; i<=n && ok==1; i++)   if(G[i].size()%2!=0)   ok=0;

    if(ok)
        euler();
    else
        putChar('-'),putChar('1');

    fwrite(outBuff, 1, buff_size, stdout);
}

int main ()
{
    read_data();
    solve();
}