#include <bits/stdc++.h>

using namespace std;
class InParser {
private:
	FILE *fin;
	char *buff;
	int sp;

	char read_ch() {
		++sp;
		if (sp == 4096) {
			sp = 0;
			fread(buff, 1, 4096, fin);
		}
		return buff[sp];
	}

public:
	InParser(const char* nume) {
		fin = fopen(nume, "r");
		buff = new char[4096]();
		sp = 4095;
	}

	InParser& operator >> (int &n) {
		char c;
		while (!isdigit(c = read_ch()) && c != '-');
		int sgn = 1;
		if (c == '-') {
			n = 0;
			sgn = -1;
		} else {
			n = c - '0';
		}
		while (isdigit(c = read_ch())) {
			n = 10 * n + c - '0';
		}
		n *= sgn;
		return *this;
	}

	InParser& operator >> (long long &n) {
		char c;
		n = 0;
		while (!isdigit(c = read_ch()) && c != '-');
		long long sgn = 1;
		if (c == '-') {
			n = 0;
			sgn = -1;
		} else {
			n = c - '0';
		}
		while (isdigit(c = read_ch())) {
			n = 10 * n + c - '0';
		}
		n *= sgn;
		return *this;
	}
};
InParser f("ciclueuler.in");
ofstream g("ciclueuler.out");
const int M=5e5+5,N=1e5+5;
struct muchie{
    int x,y;
    bool folosit;
};
int vf[2*M],urm[2*M],lst[N],nr,stiva[N];
muchie e[M];
vector <int> a[N],c;
/*void euler(int x)
{
    //for(auto i:a[x])
    for(int p=lst[x];p!=0;p=urm[p])
    {
        int i=vf[p];
        if(e[i].folosit)
        {
            continue;
        }
        e[i].folosit=true;
        int y=e[i].x+e[i].y-x;
        euler(y);
    }
    c.push_back(x);
}*/
void euler()
{
    int vf=0;
    stiva[++vf]=1;
    while (vf > 0)
    {
        int x=stiva[vf];
        bool gasit=false;
        for(int j=a[x].size()-1;j>=0;j--)
        {
            int i = a[x][j];
            a[x].pop_back();
            if(e[i].folosit)
            {
                continue;
            }
            e[i].folosit=true;
            int y=e[i].x+e[i].y- x;
            stiva[++vf]=y;
            gasit=true;
            break;
        }
        if(!gasit)
        {
            c.push_back(x);
            vf--;
        }
    }
}

/*void adauga(int x,int i)
{
    vf[++nr]=i;
    urm[nr]=lst[x];
    lst[x]=nr;
}*/
int gr[N];
int n,m;
bool verifica()
{
    for(int i=1;i<=n;i++)
    {
        if(gr[i]%2==1)
        return 0;
    }
    return 1;
}
int main()
{
    f>>n>>m;
    for(int i=0;i<m;i++)
    {
        f>>e[i].x>>e[i].y;
        gr[e[i].x]++;
        gr[e[i].y]++;
        a[e[i].x].push_back(i);
        //adauga(e[i].x,i);
        a[e[i].y].push_back(i);
        //adauga(e[i].y,i);
    }
    if(!verifica())
    {
        g<<-1;
        return 0;
    }
    euler();
    if(c.size()==m+1 && c[0]==c[m])
    {
        c.erase(c.begin()+m);
        for(auto i:c)
        {
            g<<i<<" ";
        }
    }
    else
    {
        g<<-1;
    }
    g.close();
    return 0;
}