#include <fstream>
#include <vector>
#include <bitset>

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;
	}
} f("ciclueuler.in");

class OutParser {
private:
    FILE *fout;
    char *buff;
    int sp;

    void write_ch(char ch) {
        if (sp == 50000) {
            fwrite(buff, 1, 50000, fout);
            sp = 0;
            buff[sp++] = ch;
        } else {
            buff[sp++] = ch;
        }
    }


public:
    OutParser(const char* name) {
        fout = fopen(name, "w");
        buff = new char[50000]();
        sp = 0;
    }
    ~OutParser() {
        fwrite(buff, 1, sp, fout);
        fclose(fout);
    }

    OutParser& operator << (int vu32) {
        if (vu32 <= 9) {
            write_ch(vu32 + '0');
        } else {
            (*this) << (vu32 / 10);
            write_ch(vu32 % 10 + '0');
        }
        return *this;
    }

    OutParser& operator << (long long vu64) {
        if (vu64 <= 9) {
            write_ch(vu64 + '0');
        } else {
            (*this) << (vu64 / 10);
            write_ch(vu64 % 10 + '0');
        }
        return *this;
    }

    OutParser& operator << (char ch) {
        write_ch(ch);
        return *this;
    }
    OutParser& operator << (const char *ch) {
        while (*ch) {
            write_ch(*ch);
            ++ch;
        }
        return *this;
    }
} g("ciclueuler.out");

int n, m, x[500001], y[500001];

bitset <500001> viz;

vector <int> ans, a[100001], q;

inline void euler(int nod)
{
    q.push_back(nod);

    while (!q.empty()) {
        nod = q.back();

        if (!a[nod].empty()) {
            int nodd = a[nod].back();

            a[nod].pop_back();

            if (!viz[nodd]) {
                viz[nodd] = 1;
                q.push_back(x[nodd] + y[nodd] - nod);
            }
        }
        else {
            ans.push_back(nod);
            q.pop_back();
        }
    }
}

int main()
{
    f >> n >> m;

    for (int i = 1; i <= m; ++i) {
        f >> x[i] >> y[i];

        a[x[i]].push_back(i);
        a[y[i]].push_back(i);
    }

    for (int i = 1; i <= n; ++i) {
        if (a[i].size() & 1) {
            g << -1;
            return 0;
        }
    }

    euler(1);

    for (int i = 0; i < (int) ans.size() - 1; ++i) {
        g << ans[i] << ' ';
    }

    return 0;
}