#include <cstdio>
#include <iostream>
#include <vector>
#include <queue>
#include <utility>
#include <algorithm>
#include <functional>
#include <string>
#include <cstring>
#include <cmath>
#include <map>
#include <set>
#include <bitset>
#include <stack>
#include <iomanip>
#define MOD 1000000007
#define NMAX 100005
#define INF 0x3f3f3f3f
#define pb push_back

using namespace std;

FILE *fin = freopen("ciclueuler.in", "r", stdin);
FILE *fout = freopen("ciclueuler.out", "w", stdout);

typedef pair<int, int> pii;

vector<int> v[NMAX], aux;
int nrm = 1, m;

void eulerTour(int x) {
    int y;

    while(v[x].size()) {
        y=v[x].back();

        v[x].erase(v[x].end()-1);
        vector<int>::iterator it;
        for(it=v[y].begin(); it!=v[y].end(); ++it) {
            if(*it==x) {
                v[y].erase(it);
                break;
            }
        }

        eulerTour(y);
    }

    if(nrm<m) {
        aux.push_back(x);
        ++nrm;
    }
}

int main() {
    int n, i, x, y, a, b;

    scanf("%d%d", &n,&m);
    for (i = 0; i < m; ++i) {
    scanf("%d%d", &x, &y);

        v[x].pb(y);
        v[y].pb(x);
    }

       for(i=1;i<=n; ++i) {
        if(v[i].size()%2 != 0 || v[i].empty()) {
            cout<<-1;
            return 0;
        }
    }

    eulerTour(1);

    //for(i=0;i<m;++i)
    //    printf("%d ", aux[i]);

    return 0;
}