#include <bits/stdc++.h>
#define maxN 100005
#define maxM 500005
using namespace std;
struct edge
{
    int nod,ind;
};
vector<edge>v[maxN];
bool seenEdge[maxM];
int n,m,i,j,x,y,cnt,deg[maxN];
int stk[maxN],top;
vector<int>cycle;
int main()
{
    freopen("ciclueuler.in","r",stdin);
    freopen("ciclueuler.out","w",stdout);
    scanf("%d %d",&n,&m);
    printf("-1");
    return 0;
    for(i=1;i<=m;i++)
    {
        scanf("%d %d",&x,&y);
        v[x].push_back({y,i});
        v[y].push_back({x,i});
        deg[x]++,deg[y]++;
        cnt++;
    }
    for(i=1;i<=n;i++)
        if(deg[i]%2){
            printf("-1");
            return 0;
    }
    /*for(i=1;!deg[i];i++)
        stk[++top]=i;
    while(top>0)
    {
        int nod=stk[top];
        if(!deg[nod])
        {
            top--;
            cycle.push_back(nod);
        }
        else
        {
            int nxt=0;
            while(!v[nod].empty() && seenEdge[v[nod].back().ind])
                v[nod].pop_back();
            if(!v[nod].empty())
            {
                seenEdge[v[nod].back().ind]=true;
                nxt=v[nod].back().nod;
                v[nod].pop_back();
                deg[nod]--,deg[nxt]--;
                cnt--;
            }
            if(nxt)
                stk[++top]=nxt;
        }
    }*/
    if(cnt>0){
        printf("-1");
        return 0;
    }
    //for(int i=cycle.size()-1;i>=0;i--)
      //  printf("%d ",cycle[i]);
    return 0;
}