#include <bits/stdc++.h>
using namespace std;
typedef long double ld;
typedef long long ll;
int n, m, used[10050];
vector<int> g[10050];
void dfs(int v, int p = -1) {
    used[v] = 1;
    cout << v + 1 << endl;
    for (int u: g[v]) {
        if (used[u]) {
            if (u != p && used[u] == 1)
                cout << u + 1 << endl << v + 1 << endl;
            continue;
        }
        dfs(u, v);
        cout << v + 1 << endl;
    }
    used[v] = 2;
}
int main() {
    //freopen("input.txt","r",stdin);
    //freopen("output.txt","w",stdout);
    cin >> n >> m;
    for (int i = 0; i < m; i++) {
        int u, v;
        cin >> u >> v;
        u--; v--;
        g[u].push_back(v);
        g[v].push_back(u);
    }
    cout << 2 * m << endl;
    dfs(0);
    return 0;
}