#include <bits/stdc++.h>

const int BUFFER_SIZE = 1 << 17;

char buffer[BUFFER_SIZE];
int pos = BUFFER_SIZE, nr = 0;
bool visited[(int)(1e5 + 1)];

inline char next() {
	if (pos == BUFFER_SIZE) {
		fread(buffer, 1, BUFFER_SIZE, stdin);
		pos = 0;
	}
	
	return buffer[pos++];
}

inline int read() {
	int n = 0;
	char c = next();

	while (!('0' <= c && c <= '9')) {
		c = next();
	}

	while ('0' <= c && c <= '9') {
		n = (n << 3) + (n << 1) + (c - '0');
		c = next();
	}

	return n;
}

inline void print(int n) {
	char snum[65];
	int i = 0;

	do {
		snum[i++] = n % 10 + '0';
		n /= 10;
	} while (n);

	--i;

	while (i >= 0) {
		putchar(snum[i--]);
	}

	putchar(' ');
}

void dfs(int node, std::vector<std::pair<int, int>> v[], int &m) {
	while (v[node].size()) {
		int current = v[node].back().first;
		int neighbor = v[node].back().second;
		v[node].pop_back();

		if (!visited[neighbor]) {
			visited[neighbor] = true;
			dfs(current, v, m);
		}
	}

	if (m) print(node), --m;
}

int main() {
	freopen("ciclueuler.in", "r", stdin);
	freopen("ciclueuler.out", "w", stdout);
	int n = read(), m = read();
	std::vector<std::pair<int, int>> *v = new std::vector<std::pair<int, int>> [n + 1];

	for (int i = 1 ; i <= m ; ++i) {
		int src = read(), dest = read();
		v[src].emplace_back(std::make_pair(dest, i));
		v[dest].emplace_back(std::make_pair(src, i));
	}

	for (int i = 1 ; i <= n ; ++i) {
		if (v[i].size() & 1) {
			putchar('-'), putchar('1');
			return 0;
		}
	}

	dfs(1, v, m);
	delete [] v;
	return 0;
}