#include<fstream>
#include<list>
#include<algorithm>
#define N 100001
using namespace std;
ifstream f("ciclueuler.in");ofstream g("ciclueuler.out");int n,m,i,j,v,x,y,s[N*5];list<int>l[N];int main(){f>>n>>m;while(m--)f>>x>>y,l[x].push_back(y),l[y].push_back(x);for(i=1;i<=n;++i)if(l[i].size()%2){g<<-1<<'\n';return 0;}for(v=s[1]=1;v;){for(x=s[v];!l[x].empty();)y=l[x].front(),l[x].pop_front(),l[y].erase(find(l[y].begin(),l[y].end(),x)),s[++v]=x=y;g<<s[v--]<<' ';}}