#include <stdio.h>
#include <stdlib.h>
#include <ctype.h>
#include <vector>
#include <algorithm>

#define In "ciclueuler.in"
#define Out "ciclueuler.out"

FILE *fin = fopen(In, "r"), *fout = fopen(Out, "w");

#define BUF 1 << 17
int pos = BUF;char buf[BUF];

inline char next()  {
    if(pos == BUF)
        fread(buf, 1, BUF, fin), pos = 0;
    return buf[pos++];
}

inline int read()  {
    int x = 0, semn = 1;
    char ch = next();
    while(!isdigit(ch) && ch != '-')
        ch = next();
    if(ch == '-')
        ch = next(), semn = -1;
    while(isdigit(ch))
        x = x * 10 + ch - '0', ch = next();
    return x * semn;
}

#define NMAX 100001

int N, M;

std::vector <int> G[NMAX + 1];
std::vector <int> Sol;
std::vector <int> stk;

inline void euler(int nod)  {
    stk.push_back(nod);
    while(!stk.empty())  {
        int nod = stk.back();
        while(G[nod].size())  {
            int nxt = G[nod].back();
            G[nod].pop_back();
            G[nxt].erase(find(G[nxt].begin(), G[nxt].end(), nod));
            stk.push_back(nxt);
            nod = nxt;
        }
        Sol.push_back(stk.back());
        stk.pop_back();
    }
}

int main()  {
    N = read(), M = read();

    for(int i = 0;i < M;i++)  {
        int x, y;
        x = read(), y = read();
        G[x].push_back(y);
        G[y].push_back(x);
    }
    for(int i = 1;i <= N;i++)  {
        if(G[i].size() & 1)  {
            fprintf(fout, "-1\n");
            return 0;
        }
    }

    euler(1);
    for(int i = 0;i < Sol.size() - 1;i++)
        fprintf(fout, "%d ", Sol[i]);
    fclose(fin);
    fclose(fout);
    return 0;
}