#include <iostream>
#include <stack>
#include <vector>

#define NMAX 100000
#define MMAX 500000

using namespace std;

struct muchie {
  int to ;
  int poz ;
};

stack <int> s ;
vector <muchie> g [ NMAX + 1 ] ;
int viz [ MMAX + 1 ] ;
int euler [ NMAX + 1 ] ;
int e;

void dfs (int nod ) {
  for (auto elem : g[nod] ) {
    if (!viz[elem.poz]) {
      viz[elem.poz] = 1 ;
      dfs(elem.to) ;
    }
  }
  euler[e++] = nod ;
}

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;
	}
};
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;
    }
};

int main() {

  InParser fin("ciclueuler.in" ) ;
  OutParser fout("ciclueuler.out" ) ;
  int n, m, i, u, v, ok, nod ;
  fin >> n >> m ;
  for (i = 0 ; i < m ; i++ ) {
    fin >> u >> v ;
    g[u].push_back({v, i}) ;
    g[v].push_back({u, i}) ;
  }
  ok = 0 ;
  for (i = 1 ; i <= n ; i++ )
    if (g[i].size() % 2 == 1 )
      ok = 1 ;
  if (ok == 1 )
    fout << "-1" ;
  else {
    e = 0 ;
    dfs(1) ;
    for (i = 0 ; i < e ; i++ )
      fout << euler[i] << " " ;
  }
  return 0;
}