import std.algorithm;
import std.array;
import std.ascii;
import std.bigint;
import std.complex;
import std.container;
import std.conv;
import std.functional;
import std.math;
import std.range;
import std.stdio;
import std.string;
import std.typecons;

auto readInts() {
	return array(map!(to!int)(readln().strip().split()));
}
auto readInt() {
	return readInts()[0];
}
auto readLongs() {
	return array(map!(to!long)(readln().strip().split()));
}
auto readLong() {
	return readLongs()[0];
}

void readlnTo(T...)(ref T t) {
    auto s = readln().split();
    assert(s.length == t.length);
    foreach(ref ti; t) {
        ti = s[0].to!(typeof(ti));
        s = s[1..$];
    }
}

const real eps = 1e-10;

const long p = 1_000_000_000 + 7;

int[] dfs(int[][] g, bool[] used, int x) {
    used[x] = true;
    foreach(gi; g[x]) {
        if(used[gi]) {
            continue;
        }
        return dfs(g, used, gi) ~ x;
    }
    auto ret = [x];
    ret.reserve(100000);
    return ret;
}

void main(){
    int n, m;
    readlnTo(n, m);
    auto g = new int[][](n, 0);
    foreach(_; iota(m)) {
        int a, b;
        readlnTo(a, b);
        --a;
        --b;
        g[a] ~= b;
        g[b] ~= a;
    }
    auto used = new bool[](n);
    auto a = dfs(g, used, 0);
    used[0] = false;
    auto b = dfs(g, used, 0);
    b.reverse();
    b = b[1..$];
    writeln(a.length + b.length);
    a.each!(a => write(a+1, " "));
    if(!b.empty) {
        b[0..$-1].each!(a => write(a+1, " "));
        writeln(b[$-1]+1);
    }
}

